Just like they did in 2016:

George Santos inspired no shortage of suspicion during his 2022 campaign, including in the upper echelons of his own party, yet many Republicans looked the other way.

In late 2021, as he prepared to make a second run for a suburban New York City House seat, George Santos gave permission for his campaign to commission a routine background study on him.

Campaigns frequently rely on this kind of research, known as vulnerability studies, to identify anything problematic that an opponent might seize on. But when the report came back on Mr. Santos, the findings by a Washington research firm were far more startling, suggesting a pattern of deception that cut to the heart of the image he had cultivated as a wealthy financier.

Some of Mr. Santos’s own vendors were so alarmed after seeing the study in late November 2021 that they urged him to drop out of the race, and warned that he could risk public humiliation by continuing. When Mr. Santos disputed key findings and vowed to continue running, members of the campaign team quit, according to three of the four people The New York Times spoke to with knowledge of the study.

The episode, which has not been previously reported, is the most explicit evidence to date that a small circle of well-connected Republican campaign professionals had indications far earlier than the public that Mr. Santos was spinning an elaborate web of deceits, and that the candidate himself had been warned about just how vulnerable those lies were to unraveling.

Fraudulent academic degrees. Involvement in a firm accused of a Ponzi scheme. Multiple evictions and a suspended driver’s license. All of it was in the report, which also said that Mr. Santos, who is openly gay, had been married to a woman. The report did not offer conclusive details, but some people briefed on the findings wondered whether the marriage was done for immigration purposes.

It remains unclear who else, if anyone, learned about the background study’s contents at the time, or if the information made its way to party leaders in New York or Washington. Mr. Santos, 34, managed to keep almost all of it from the public until after he was elected, when an investigation by The Times independently unearthed the problematic claims documented by researchers and others that they missed.

After The Times sent a detailed list of questions for this story, a lawyer for Mr. Santos, Joe Murray, said “it would be inappropriate to respond due to ongoing investigations.” A spokeswoman for Mr. Santos’s congressional office did not respond to a similar request for comment.

Mr. Santos himself has admitted to some fabrications, but insists he was merely embellishing his qualifications. He has vowed to serve out a two-year term in Congress. State, local and federal prosecutors are now investigating his activity.

The existence of the vulnerability study underscores one of the most vexing questions still surrounding the strange saga of George Santos: How did the gate-keeping system of American politics — Republican leaders, adversarial Democrats and the prying media — allow a fabulist who boasted about phantom mansions and a fake résumé get away with his con for so long?

Interviews with more than two dozen associates, adversaries and donors, as well as contemporaneous communications and other documents reviewed by The Times, show that Mr. Santos inspired no shortage of suspicion during his 2022 campaign, including in the upper echelons of his own party.

Well-connected supporters suspected him of lying and demanded to see his résumé. Another former campaign vendor warned a state party official about what he believed were questionable business practices. And the head of the main House Republican super PAC told some lawmakers and donors that he believed Mr. Santos’s story did not add up.

But in each case, rather than denounce Mr. Santos publicly, the Republicans looked the other way. They neglected to get the attention of more powerful leaders or to piece together shards of doubt about him, and allowed him to run unopposed in the 2022 primary. Some assumed that Mr. Santos’s falsehoods were garden variety political embellishments; others thought Democrats would do their dirty work for them and Mr. Santos would be exposed in the heat of a general election campaign.

But Democrats struggled to do so. In 2020, the party incumbent, Tom Suozzi, dismissed Mr. Santos as a nonviable threat, and conducted no opposition research at all while cruising to victory. When Democrats did vet him two years later, they failed to find some of the most egregious fabrications that prompted members of Mr. Santos’s campaign team to quit.

Democrats then labored unsuccessfully to convince the news media, which had been weakened by years of staff cuts and consumed by higher-profile races, to dig into the troubling leads they did unearth. Aside from The North Shore Leader — a small weekly newspaper on Long Island, which labeled Mr. Santos “a fake” — and a few opinion pieces in Newsday, New York’s media machine paid Mr. Santos scant attention.

“The reality is there’s no defense, it shouldn’t have happened,” said Gerard Kassar, the chairman of the New York Conservative Party, a small but influential partner to the Republican Party that backed Mr. Santos. “It would be impossible and probably incorrect for me to say this could never happen again, but it won’t be from me not looking again.”

Mr. Santos was a political neophyte when he first showed interest in running for a House seat made up of parts of Queens and Nassau County in 2020. His only real electoral experience ended quickly: A year earlier, he was forced to drop his insurgent campaign for a low-level party position in Queens because he lacked enough valid signatures to make the ballot, according to Joann Ariola, a New York City Council member who led the Queens Republican Party at the time.

Among the tight-knit Republican circles on Long Island, he was virtually unknown. And in Queens, party leaders were still sour over his initial foray.

In normal circumstances, Mr. Santos would have been shooed away. Republicans in Nassau County, which comprises the bulk of New York’s Third Congressional District, have long been famous for exercising tight control over who runs, grooming and rewarding a stable of candidates like an old-school political machine.

But with the country in lockdown in the early days of the coronavirus pandemic and the district expected to remain under Democratic control, no one else put their hand up to run. Mr. Santos submitted a résumé and answered a vetting questionnaire riddled with lies, including that he had a 3.9 grade-point average from a college he never graduated from and job credentials he did not possess. A vetting team for the county Republican Party accepted his answers without question.

“I guess unfortunately we rely on the person to be truthful to us,” Joseph G. Cairo Jr., the Republican Party county chairman, said in an interview. This week, he called on Mr. Santos to resign and said he would no longer be welcome in the Nassau Republican Party.

When Mr. Santos chose to run again two years later, local Republicans again gave him their support. They expected that flipping the district would once again be a stretch and, in any case, Mr. Cairo’s priority was winning state and local offices, which control thousands of local jobs and major tax and spending decisions. Efforts to recruit a more formidable candidate, like State Senator Jack Martins, did not pan out.

There were already questions swirling by that time among donors and political figures about where exactly Mr. Santos lived and the source of the money that supported the lavish lifestyle he boasted about.

In the summer of 2021, one of the former advisers to Mr. Santos, who insisted on anonymity, discovered his connections to Harbor City Capital, the Florida-based firm accused of a Ponzi scheme, and to other suspicious business practices that Mr. Santos had obscured. The adviser said he took the findings to a state party official later that fall and tried to pitch the story to a newspaper, which he said did not pursue it. The Harbor City connection was later reported in The Daily Beast.

Around that time, Mr. Santos began attracting the suspicion of a pair of friends and potential donors active in New York Republican circles. Mr. Santos claimed to one of them, Kristin Bianco, to have secured the endorsement of former President Donald J. Trump, when he had not. That prompted her to express concerns about Mr. Santos to plugged-in Republicans, including associates of Representative Elise Stefanik of New York, one of Mr. Santos’s biggest early backers whose top political aide was assisting his campaign. Later Ms. Bianco and her friend became suspicious that they could not verify his work history.

“We’re just so tired of being duped,” Ms. Bianco texted Mr. Santos in early 2022, after he refused her request to produce his résumé. Mr. Santos wrote back that he found the request “a bit invasive as it’s something very personal.”

In the run-up to the 2022 contest, Dan Conston, a close ally of Speaker Kevin McCarthy who leads the Congressional Leadership Fund, the main House Republican super PAC, also confided in lawmakers, donors and other associates that he was worried information would come out exposing Mr. Santos as a fraud, according to two people with knowledge of the conversations who insisted on anonymity to describe them and declined to provide more detail.

In the spring of 2022, Mr. Santos’s race suddenly became competitive, after a state court undid a Democratic gerrymander and adopted new congressional boundaries friendlier to Republicans. Despite the prime pickup opportunity, the Congressional Leadership Fund deliberately withheld support from the contest — but never spoke about it publicly. A spokesman for Mr. Conston’s group declined to comment on its campaign strategy or its leaders’ conversations.

If party leaders were aware of any of the concerns about Mr. Santos, or others raised by his former vendors, they found ways to reassure themselves.

“The thinking was the guy went through a campaign with Suozzi, who was a pretty tough and thorough guy,” said Peter T. King, a retired longtime Republican congressman from Nassau County. “So anything would have come out.”

The assumption that any damaging information about Mr. Santos would have been found in the 2020 campaign turned out to be misguided.

Mr. Suozzi, the popular Democratic incumbent, got a quote for the cost of an outside firm to do opposition research on Mr. Santos. But he decided not to spend the money — sparing Mr. Santos meaningful scrutiny in his first race.

“No one knew George Santos, and he had less than $50,000 in campaign funds against a popular incumbent who never even said his name,” said Kim Devlin, a Suozzi adviser. “We didn’t feed anything to the press because why would we give him press?”

With a more competitive race expected in 2022, researchers at the Democratic Congressional Campaign Committee did the first meaningful opposition research on Mr. Santos that summer, assembling an 87-page opposition research book. It extensively documents Mr. Santos’s past statements — including his extreme views on abortion rights and the Jan. 6 Capitol riot.

Mr. Santos’s 2022 opponent, Robert Zimmerman, got hold of the research book in late August, right after he won a competitive and costly Democratic primary. He decided not to spend what would have likely been tens of thousands of dollars to do more rigorous outside research.

Other Democrats have second-guessed that decision in recent weeks, but at the time, Mr. Zimmerman had his reasons. While presidential and Senate campaigns typically have the financial and staff resources for exhaustive opposition research, House campaigns tend to rely on the D.C.C.C. to conduct their research.

Strapped for time and cash, Mr. Zimmerman concluded that his money would be better spent on advertising and canvassing operations. And he believed that the campaign committee’s report as well as Mr. Santos’s far-right views on abortion and Jan. 6 — two of the year’s most prominent campaign themes — gave him powerful campaign fodder.

“We knew a lot about him did not add up; we were very conscious of that,” Mr. Zimmerman said in an interview. “But we didn’t have the resources as a campaign to do the kind of digging that had to be done.”

Mr. Zimmerman said his campaign tried to prod reporters at local and national news outlets with leads about Mr. Santos, but had little luck. The candidate himself, a public relations executive, did not hold news conferences or use paid advertising to draw attention to known discrepancies in his opponent’s record.

“The response we got back pretty universally was they just didn’t have the personnel, the time or the money to do it,” Mr. Zimmerman said, referring to the publications the campaign contacted. “One person said to me, there are 60 to 80 crazy people running, we can’t investigate them all.”

One outlet stood out, The North Shore Leader in Long Island, run by a Republican lawyer and former House candidate, Grant Lally. The paper published a pair of articles casting doubt on Mr. Santos’s claims that he owned extravagant cars and homes, and labeling him a “fabulist — a fake,” though it did not have other specifics that would later come out about his falsified résumé or his past.

None of the bigger outlets, including The Times, followed up with extensive stories examining his real address or his campaign’s questionable spending, focusing their coverage instead on Mr. Santos’s extreme policy views and the historic nature of a race between two openly gay candidates.

What did top Republicans know?

In the aftermath of Mr. Santos’s exposure, Democrats have said that their researchers would likely not have turned up much of the information uncovered by The Times and other media outlets after the election. Private institutions like schools and businesses are more inclined to share educational and employment records with reporters than with political parties, they say.

But the opposition research firm Mr. Santos hired in the fall of 2021 — his campaign reported spending $16,600 on Capital Research Group LLC — seems to have had relatively little trouble turning up some of that same information.

People working for his campaign had grown accustomed to Mr. Santos’s braggadocio and outlandish claims. But when they approached him about conducting a vulnerability study, the objective was more routine: producing a record of his past statements and other public information that would be useful later when his opponents started crafting attacks.

Mr. Santos quickly signed off, but as the research dragged on, he asked to cancel the contract with the firm. When the results came back, it was clear why.

Researchers found no evidence that Mr. Santos had earned degrees at Baruch College and New York University, as he had claimed. They turned up records showing his involvement with the company accused of a Ponzi scheme — a relationship he had played down. They found eviction records, business records and a suspended Florida driver’s license, which together raised questions about whether he was a legal New York resident and as rich as he claimed to be.

The report also said that Mr. Santos, who was openly gay and appeared to be living with a man at the time, had been married to a woman. The study missed other fabrications that The Times later uncovered, including false claims that he worked at Citibank and Goldman Sachs. Nor did it turn up records of fraud charges in Brazil years earlier.

The Times has not seen the vulnerability study, but it was described in recent days by four people with knowledge of the report who were granted anonymity because it remains confidential.

The people working for Mr. Santos convened an emergency conference call to discuss the results on Dec. 1, 2021. They presented him with a choice: bow out of the race with dignity, or stay in and risk letting the Democrats turn up the same information and use it to destroy his political and personal future.

After promising to produce diplomas that would prove his degrees (he ultimately did not), Mr. Santos said he would think it over. When he came back a few days later, he said he had spoken with other advisers and was convinced the findings were not as bad as they were being portrayed. He was staying in the race. Most of his team quit.

What top Republicans were told of Mr. Santos’s issues is more difficult to chart. Mr. Santos required those working for his campaign to sign nondisclosure agreements, limiting the spread of the vulnerability report. But one person who was briefed on its contents said that questions about Mr. Santos’s background were discussed well beyond campaign vendors. The National Republican Congressional Committee, which closely monitors House candidates and backed Mr. Santos, sometimes requests such reports as a condition of its support.

A spokesman for the group declined to comment for this article, but pointed to an earlier statement denying it had previous knowledge that Mr. Santos’s record was largely fabricated. The N.R.C.C. typically does not conduct its own independent vulnerability studies on candidates.

Mr. McCarthy, who ultimately endorsed Mr. Santos and helped his campaign, has said relatively little about the fabrications, and has refused calls to try to oust him from the House as the speaker seeks to maintain an exceedingly narrow majority in Washington. This week, Mr. McCarthy played down Mr. Santos’s lies, comparing them to other politicians who have embellished parts of their résumés and implying he would not undo the will of voters who elected him.

Spokesmen for Mr. McCarthy did not respond to repeated requests for comment for this story, and a spokesman for Ms. Stefanik, the highest-ranking New York House Republican, declined to comment. Allies of Mr. McCarthy maintain that they did not know about the baldest fabrications and misrepresentations, like those turned up by Republican researchers in late 2021, but only had more general concerns about his honesty.

Despite the financial resources he helped marshal to the race, Mr. McCarthy had good personal reason to be wary of Mr. Santos. Earlier in 2021, an aide to the candidate was caught impersonating Mr. McCarthy’s chief of staff while soliciting campaign contributions.

By the spring of 2022, Mr. Santos was in need of a new team of consultants. With help from Ms. Stefanik’s top political aide, he chose a new consulting firm and shared the vulnerability study.

The new crop of vendors, led by Big Dog Strategies, never spoke to their predecessors, though, and did not know why they had left the campaign. After Mr. Santos again insisted he had graduated from college, and addressed other red flags raised in the report, the new team accepted his explanations and began plotting a campaign. They would use issues — not the candidate’s biography — to win the race.

A month before George Santos was elected to Congress, one of his large donors received a call asking him to consider making another sizable contribution.

The request came from a Republican loyalist calling on behalf of RedStone Strategies, which was described in an email to the donor as an “independent expenditure” group that was supporting Mr. Santos’s bid to flip a Democratic House seat in New York. The group had already raised $800,000 and was seeking to raise another $700,000, according to the email, which was reviewed by The New York Times.

The donor came through: Days later, on Oct. 21, he sent $25,000 to a Wells Fargo Bank account belonging to RedStone Strategies.

Three months later, Mr. Santos is now in Congress, but where the donor’s money went is unclear. The Federal Election Commission said it had no evidence that RedStone Strategies was registered as a political group, and there do not appear to be any records documenting its donors, contributions or spending.

Mr. Santos and his lawyer refused to answer questions about RedStone’s fund-raising efforts, but it appears that Mr. Santos was directly involved in at least one donor solicitation. He also has ties to a Redstone Strategies LLC, registered to an address in Merritt Island, Fla., in November 2021, as Mr. Santos was preparing his second run for Congress. The firm listed the Devolder Organization, a company owned by Mr. Santos, as one of its managing officers.

A company website describes that Redstone as being run by “experters in marketing and others in politics” whose services in ad creation, communications and fund-raising have value “no matter if you are in a local race or if you are going to be the next president of the United States.”

Yet the firm’s body of work — at least for candidates and committees that are required to file campaign expense reports — appears limited. A Times search of campaign finance records uncovered payments from a failed House candidate on Long Island and two groups tied to New York legislative candidates.

It also shows a payment from a PAC called Rise NY, run by Mr. Santos’s sister, Tiffany. State records show the group sent a wire transfer for $6,000 in April 2022 to Red Stone Strategies. It listed a Wells Fargo Bank branch on Merritt Island as its address.

The murkiness around the fund-raising operations on behalf of Mr. Santos makes it difficult to know whether any laws were broken. But a close examination of available records suggest RedStone may have skirted the law.

The email to the donor described it as an “independent expenditure committee under federal campaign finance law” with the “singular purpose” of electing Mr. Santos.

Such groups, also known as super PACs, can support candidates by raising vast sums of money far beyond strict campaign donor limits. Even so, there are rules: They must register with the Federal Election Commission and disclose their donors. And they must not coordinate directly with campaigns.

Yet the F.E.C. has no record of RedStone Strategies. The Daily Beast has reported that Redstone Strategies LLC of Florida had a connection to Mr. Santos, but the existence of a group operating under the name RedStone raising large sums of money for his election has not previously been revealed.

“I don’t see a record by a committee of that name registered with the F.E.C., and our regulations would be if a political group raises more than $1,000 for the purpose of influencing a federal election, they would be required to register with the F.E.C. within 10 days,” said Christian Hilland, an F.E.C. spokesman.

The person who solicited the donor said he was asked by Mr. Santos in the weeks leading up to the campaign to approach donors, some of whom had already given the maximum allowed to Mr. Santos’s election campaign, and to help coordinate their donations to RedStone, according to a person familiar with the arrangement who wished to remain anonymous.

Mr. Santos seems to have played a more direct role in at least one of the solicitation efforts.

On Thursday, another large donor to Mr. Santos said that he was asked in September to make a sizable donation to a similarly named group, Redstone Action, and was told that other donors had “made six-figure contributions.”

In an email to that donor, Redstone was described as “a 501(c)4 political organization formed specifically to influence the election in NY-03,” and the donor was told that should he decide to contribute, he should send the money directly to the same Wells Fargo Bank account that the first donor used.

The second donor, who asked not to be identified, said that he did not give the group any money. In November, the donor said he was solicited again to give to Redstone, now named RedStone Strategies — this time directly by Mr. Santos.

The donor said Mr. Santos asked for a few hundred thousand dollars that would be spent on ads attacking his opponent.

If RedStone were a registered super PAC, Mr. Santos’s involvement would violate rules prohibiting coordination between a candidate and the fund-raising group.

A lawyer for Mr. Santos declined to respond to The Times’s questions about RedStone, saying that “it would be inappropriate to respond to anything related to this apparent investigation of my client’s campaign finances.”

Mr. Santos’s finances have come under scrutiny after The Times reported last month that his successful run for Congress in New York was built on lies, including fabrications of real estate fortune, academic distinction and a glittering career on Wall Street.

Much about his web of personal and political entities — and whether or how they are in fact interrelated — is still unknown and has attracted interest from local state and federal investigators. His sudden claim to wealth has also raised questions.

According to financial disclosures that he filed as a candidate, Mr. Santos claimed that he went from earning $55,000 to running a company worth more than a million dollars in just a few years. That ostensibly enabled him to lend his campaign more than $700,000 — slightly less than the amount that RedStone Strategies claimed to have raised.

Mr. Santos’s campaign spending has also come under question, with scores of expenses for $199.99 — exactly one cent below the threshold for requiring receipts. The suspicious spending pattern served as a partial basis of a complaint that the Campaign Legal Center filed on Monday with the Federal Election Commission, accusing Mr. Santos of not only using campaign funds for personal use and misrepresenting spending but also of scheming to obscure the true source of his campaign funding.

The fund-raising efforts by RedStone Strategies seem equally opaque.

The person who solicited the $25,000 donation to RedStone has been active in the Queens Republican Party and described himself as Mr. Santos’s friend.

The donor, who did not wish to be identified, confirmed that he was told by the Queens Republican operative that the $25,000 that he gave to RedStone in October would be used as part of a large ad buy for Mr. Santos.

But the donor said he did not hear anything back on how the funds were spent. A review of spending by the company AdImpact does not show the group making any ad buys on Mr. Santos’s behalf, nor did it show any spending for Mr. Santos from other independent groups in the months leading up to Election Day.

If a group raised money under false political pretense, that activity could lead federal election officials to regard it as what is commonly known as a “scam PAC” — a group that raises money without spending it on the stated political purpose, a practice that is increasingly a concern of the F.E.C., Mr. Hilland said.

Redstone Strategies LLC of Florida listed one other manager in its incorporation records: Jayson Benoit, a business partner of Mr. Santos and former colleague at Harbor City Capital, which shut down after the S.E.C. filed a lawsuit accusing it of operating as a Ponzi scheme. (Neither Mr. Santos nor Mr. Benoit, who did not respond to requests for comment, were named in that suit.)

Another potential area of concern about RedStone Strategies was the way it was described in its donor solicitation email as a 501c4 — a type of tax-exempt group organized for the promotion of social welfare. These entities pay no federal taxes and may engage in politics so long as their major purpose is not electing candidates to office.

“They can spend up to 49.9 percent of their budget on candidate election work,” explained Paul S. Ryan, an expert in federal election law, who added that political spending was allowed as long as it was not the group’s primary purpose.

But while the donor email describes the group as a 501c4, it also pledges to dedicate “all its resources” to electing Mr. Santos — language that Mr. Ryan suggested was troubling.

“You can get away with it if you are not foolish enough to put in writing that you’re all about candidate elections,” Mr. Ryan said.

RedStone Strategies was not the only group whose activity raised warning flags among campaign finance experts.

Rise NY is a state PAC created in December 2020 by Mr. Santos’s campaign treasurer, Nancy Marks, and his sister. A Twitter profile of the group describes its purpose as “new voter registration & education as well as raising election awareness & voter enthusiasm.” The PAC raised vast sums from donors who had otherwise maxed out donating to Mr. Santos’s campaign, as reported by Newsday. One donor contributed $150,000, according to New York State Board of Election records, well beyond the limits of $2,900 per election placed on federal campaign contributions for direct campaign activity.

Social media posts show that Rise NY organized demonstrations and voter registration events on Long Island. In a Twitter post from August 2021, Rise NY claimed it had “pulled in 7800+ new Republican voters on LONG ISLAND, NY alone.”

A close examination of the group’s spending, however, reveals that many of Rise NY’s actions would be considered unusual, if not a violation. PACs like Rise NY are allowed under New York State law to give directly to candidates or authorized committees, but may not spend in other ways to help a campaign.

Yet Rise NY issued payments for wages and professional services to Santos campaign workers, including Mr. Santos’s press secretary. It also directed $10,000 in payments to a company run by Ms. Marks, the campaign treasurer. And Ms. Santos earned $20,000 for her work as the PAC’s president. She did not respond to a request for comment.

Its expenditures took place at many of the spots that Mr. Santos’s campaign filings show he liked to frequent, including Il Bacco, a restaurant in Queens where his campaign spent roughly $14,000, and an Exxon Mobil gas station that is a two-minute drive from his former apartment in Whitestone, Queens.

One donor said that he gave to the PAC after being contacted by Samuel Miele, who said in an email that he was the vice president of Rise NY. Mr. Miele was also working directly for Mr. Santos, but was later fired after he was caught impersonating a staffer for Representative Kevin McCarthy, at the time the Republican minority leader, in a fund-raising appeal, several people close to the campaign said.

A company that Mr. Miele manages, the One 57 Group, was paid $43,000 by the Santos campaign and nearly $10,000 from Rise NY PAC. Mr. Miele did not respond to requests for comment.

Two former consultants to the Santos campaign who requested anonymity in order to speak freely about their former client said that they were concerned about the close arrangement between the campaign and Rise NY, and told Mr. Santos that he should shut it down. A third former consultant turned down what it described as a lucrative offer from Mr. Santos to fund-raise for the PAC, citing legal concerns.