Rosalynn Carter, the most politically active first lady since Eleanor Roosevelt, died at 96.

Rosalynn Carter, a true life partner to Jimmy Carter who helped propel him from rural Georgia to the White House in a single decade and became the most politically active first lady since Eleanor Roosevelt, died on Sunday in Plains, Ga. She was 96.

Historian Michael Beschloss revealed on MSNBC that when former President Jimmy Carter was at his sickest, and they feared the worst, he refused to go into the hospital and leave her side.

Rosalynn Carter died with her loving husband holding her hand. The two had been in hospice as she suffered from dementia and he had his own health issues.

"Number one, this was one of the great marriages in American history, even if they weren't president and first lady," said Beschloss. "Not only the length of this marriage, (77 years) but the closeness of it — that partnership. And you know, everyone who has said this in the last two minutes is absolutely right. They love most of all being with each other. I am told by someone who is very close to both Carters, that last winter, when Jimmy Carter was told that he was very sick and there was not very much that could be done for him, he was told, probably the best thing is for you to go into the hospital where you can get the best care. And I am told that President Carter said, no, I want to get home, and be in bed with Rosalynn, and just sit holding hands, and that's the way I'd like to close my life. And that's really the way it happened."

Beschloss went on to talk about the powerful role that Mrs. Carter played in the presidency and that it was more of a dual presidency like what was seen with President Franklin D. Roosevelt and Eleanor Roosevelt. "And I mean that in the most admiring way possible," he explained.

Beschloss went on to say that when he would ask her about her impact, and she would downplay it, modestly saying she only provided advice from time to time.

"This was really a mom-and-pop shop," he said of Carter's presidency. He explained she was very "good at concealing" that fact.

Richard Lui later classified the Carter presidency as the one with the most PDA (public displays of affection).

Mrs. Carter was the second longest-lived first lady; Bess Truman, the widow of President Harry S. Truman, was 97 when she died in 1982.

Over their nearly eight decades together, Mr. and Mrs. Carter forged the closest of bonds, developing a personal and professional symbiosis remarkable for its sheer longevity.

Their extraordinary union began formally with their marriage in 1946, but, in a manner of speaking, it began long before that, with a touch of kismet, just after Rosalynn (pronounced ROSE-a-lynn) was born in Plains in 1927.

She had been delivered by Mr. Carter’s mother, a nurse. And a few days later, in a scene that might have been concocted by Hollywood, his mother took little Jimmy to Rosalynn’s house, where he “peeked into the cradle to see the newest baby on the street,” as he recalled in his 2015 memoir, “A Full Life, Reflections at Ninety.”

He was not quite 3. Eighteen years would pass before the two would truly connect. But once they did, they became life and work partners, melding so completely that as president Mr. Carter would call her “an almost equal extension of myself.”

As a teenager, while Jimmy was a midshipman at the U.S. Naval Academy in Annapolis, Md., Rosalynn developed a crush on him — she had seen a picture of him in his Navy uniform on Ruth’s wall. Rosalynn and Ruth conspired for years to get him to notice her, but after his fateful glimpse of her as a newborn, they had few encounters.

The Smiths were not as well off as the Carters. Rosalynn was 13 when her father died of leukemia, and her mother was left with an insurance policy that paid $18.75 a month. Rosalynn helped with the sewing and housekeeping and with raising her siblings. She also worked at the local beauty parlor, shampooing hair.

Despite her hardships and obligations, she was valedictorian of her class at Plains High School. She later commuted to Georgia Southwestern College, then a junior college (now Georgia Southwestern State University), in nearby Americus.

In 1945, when Mr. Carter was home on leave, he finally noticed Rosalynn and asked her out. She said yes.

“She’s the girl I want to marry,” he told his mother after that first date.

He later wrote, “She was remarkably beautiful, almost painfully shy, obviously intelligent, and yet unrestrained in our discussion on the rumble seat of the Ford Coupe.”

To Rosalynn, this upwardly mobile midshipman represented an escape from the small-town life that seemed to be her fate.

When she visited him at Annapolis that winter, he proposed, but she turned him down; she had promised her father on his deathbed that she wouldn’t marry until she finished college.

By summer, they had both graduated, she from junior college and he from Annapolis. They married on July 7, 1946. She was 18, he was 21.

Reared in the same tiny patch of Georgia farmland, 150 miles south of Atlanta, they were similar in temperament and outlook. They shared a fierce work ethic, a drive for self-improvement and an earnest, even pious, demeanor. Their Christian faith was central to their lives. Both were frugal. Both could be stubborn.

The couple moved to Norfolk, Va., where Mr. Carter was stationed, though they would soon hopscotch across the country. The birthplaces of their three sons reflected their varied postings: John William was born in Virginia in 1947; James Earl III in Hawaii in 1950; and Donnel Jeffrey in Connecticut in 1952. (Their daughter, Amy, was born in Plains in 1967, long after Mr. Carter had left the Navy.)

In addition to her husband, Mrs. Carter is survived by her four children; 11 grandchildren; 14 great-grandchildren, and her sister, Lillian Allethea Smith Wall. Her brothers, Murray and Jerrold, both died in 2003.

While in the Navy, Mr. Carter was away at sea much of the time. Although Mrs. Carter struggled at home alone with their young boys, she liked seeing the country and became increasingly confident and independent.

But when Mr. Carter’s father died in 1953 and her husband told her that they were moving back to Plains to take over the family peanut business, Mrs. Carter became distraught. She cried and screamed, she recalled in her memoir. She couldn’t bear the thought of returning to the small town they had left, or of living so close to her strong-willed mother and her strong-willed mother-in-law.

“It was the most serious argument of our marriage,” she wrote.

And one she lost.

Back in Plains, she was miserable and mostly stayed at home. Neighbors complained that she was aloof. The farm sputtered in a drought.

Eventually, Mrs. Carter eased into the financial side of the business, keeping the books and paying the bills. As she started advising her husband, their professional partnership began to develop, and she helped build the company into a lucrative farm supply business. It was a turning point in their relationship.

Politics Beckons

The civil rights movement brought upheaval to the South in the early 1960s. The Carters, unlike many of their neighbors, supported school desegregation, and Mr. Carter was inspired to run for office. He won a seat in the Georgia State Senate and in 1966 lost his first try for the governorship. Throughout those tumultuous years, Mrs. Carter continued to manage the business. Importantly, she overcame her terror of public speaking and immersed herself in her husband’s campaigns, helping him win the governor’s race in 1970.

After Mr. Carter defeated Gerald R. Ford for president in 1976, Mrs. Carter brought a modesty to the White House, in stark contrast to the imperial presidency of the disgraced Richard M. Nixon, whose resignation had put Ford, his vice president, into the Oval Office.

On Inauguration Day, the Carter family walked down Pennsylvania Avenue to No. 1600. Only Thomas Jefferson had made that trek on foot before them, in 1801; the Carters’ decision began a tradition that the nation now expects of its newly minted first families.

Rosalynn was rarely included on any list of best-dressed first ladies. She was not generally called “stylish” or “trendsetting.” She did not play the White House dress-up game, at least as designed by predecessors such as Dolley Madison and Jackie Kennedy. Most of the time, she seemed to actively reject it.

But that does not mean Mrs. Carter did not fully understand the power and political use of clothes, or how to strategically deploy them during her time in Washington. In fact, it is possible to see her time as first lady as a blueprint for an alternative approach to image-making that is still being used today.

Starting with Mrs. Carter’s declaration, after Jimmy Carter was elected in 1976, that the one item she would be taking with her to the White House from Georgia was her sewing machine. As a symbol, it was a succinct message to anyone listening that this was, indeed, a recession-era administration that would prioritize economy and accessibility. It was also a nod to her own folksy roots as the daughter of a dressmaker. And it set the tone for what came next — which was the greatest dressing scandal of the administration.

That took place during the 1977 inauguration, after the Carters had made history by becoming the first first couple to walk rather than ride during the inaugural parade. (Mrs. Carter’s stroll-appropriate high-neck teal cloth coat by Dominic Rompollo, a New York designer, knee-high leather boots and leather gloves all look notably modern.)

Instead of wearing a new gown to the inaugural balls, Mrs. Carter wore the same caftan-like, high-neck, gold-embroidered blue chiffon dress by Mary Matise she had bought and worn to Mr. Carter’s 1971 inauguration as governor of Georgia.

Shock and horror was the general reaction. Used clothes at the inauguration! Despite the fact that Mrs. Carter added a new gold-trimmed cape to gussy it up a bit, also by Mr. Rompollo and purchased through Jason’s, a store in Americus, Ga., The New York Times labeled the dress “old” and called Mrs. Carter a “sentimentalist” for wearing the frock again. The new first lady’s support for Seventh Avenue was questioned as the fashion industry humphed its disdain, as was her ability to represent the United States with befitting glamour on the world stage — despite the fact that glamour had never been the Carters’ sell in the first place. Down-home morality was more like it.

To that end, the inauguration dress and the values it represented established the precedent for Mrs. Carter’s stint in the White House. She continued to shop off the rack — another favorite boutique had been A. Cohen & Sons, likewise in Americus — and she decorated the White House for Christmas with pine cones, peanuts and egg shells.

But she also continued to break sartorial rules, becoming the first first lady (yet another in her litany of firsts) to establish an office in the East Wing, not to mention the first to carry a briefcase to work every morning. A briefcase!

Perhaps understanding that such an obvious sign of her more active advisory role in the administration might be as startling to the general electorate as her shopping her closet, Mrs. Carter was careful to pair that potentially controversial office accessory with more traditional shirtwaists, often detailed with pie-crust collars or other more classically feminine frills, often in colors like lilac and fuchsia — clothes more often associated with well-behaved homemakers as opposed to policymakers. Nina Hyde of The Washington Post called them “pretty and neat, comfortable and appropriate and always American made.”

They looked modest, in every sense of the word, which was also the ethos of the Carter administration.

The Carters were, of course, replaced by the Reagans, whose approach to executive office showmanship was pretty much the opposite of “modest.” Mrs. Carter’s just-folks style of dress was relegated to the status of cautionary tale in the political playbook. Conventional wisdom had it that the American people simply didn’t want their first hostess to look quite so much like them after all — at least not once she (or her husband) had been elected.

Yet just as history has become kinder to the Carter administration, and Mr. Carter himself has become something of a model of an ex-president, it is also true that Mrs. Carter’s style as first lady suddenly looks unexpectedly relevant. After all, Jill Biden, the current resident of the East Wing, is also known for her folksiness, fondness for shirtwaists, lack of interest in telegraphing her fashion choices, and penchant for appearing in the same thing twice. Or three times.

In fact, she is celebrated for it, though the watching world no longer calls it wearing old clothes. They call it sustainability. And Rosalynn Carter did it — yes — first.

The Carters sent their daughter to public school. They also brought her nanny, Mary Prince, to Washington. Ms. Prince had been wrongly convicted of murder in Georgia and, under a work-release program, assigned to work in the governor’s mansion. With Mrs. Carter’s help, she received a reprieve so that she could move into the White House, a move enabled by Mr. Carter’s having himself designated to be Ms. Prince’s parole officer. After a later re-examination of the evidence in her case, she received a full pardon.

After Mr. Carter lost his re-election bid in 1980 to Ronald Reagan, he and Mrs. Carter embarked on what became the longest, most active post-presidency in American history. They traveled the world in support of human rights, democracy and health programs; domestically, they labored in service to others, most prominently pounding nails to help build houses for Habitat for Humanity.

In October 2019, after more than 73 years of marriage, they became the nation’s longest-married presidential couple, surpassing the record set by George H.W. Bush and Barbara Bush. The Carters marked their 77th wedding anniversary in July.

In the continuum of first ladies after Mrs. Roosevelt, Mrs. Carter broke the mold. Like most of the others, she championed a cause — hers was the treatment of mental illness. But she also immersed herself in the business of the nation and kept a sharp eye on politics, a realm her husband famously claimed to ignore.

She frequently attended Mr. Carter’s cabinet meetings and traveled abroad to meet with heads of state in visits labeled substantive, not ceremonial. She often sat in on the daily National Security Council briefings held for the president and senior staff.

The couple held a weekly working lunch to discuss policy. Mrs. Carter testified before Congress and lobbied its members. Her handwriting appears on the drafts of many of her husband’s speeches and policy addresses.

Though soft-spoken, she was nevertheless assertive about her power and influence in public affairs.

“When I come home very discouraged,” Mr. Carter told The New York Times in 1979, “she listens to only just a few words and she looks around at me and says that I’ve got a problem with this or that. She knows enough about the background of that problem that I don’t have to sit for two hours and explain it to her.”

A full 16 years before Bill and Hillary Clinton would offer themselves to the nation as a package deal with the slogan “Buy one, get one free,” the Carters functioned as near co-presidents. The New York Times columnist Tom Wicker wrote in 1979 that Mrs. Carter “may be the most powerful first lady since Edith Bolling Wilson virtually took over for a stricken president,” Woodrow Wilson.

Mrs. Carter entered the White House at the height of the women’s movement and seemed to derive strength from it, though she did not identify herself as a feminist. She lobbied vigorously for the Equal Rights Amendment and for women to participate at all levels of government, from honor guard at the White House to justice of the Supreme Court. She had her staff assemble a roster of qualified women for various appointments, according to the National First Ladies’ Library, and she suggested candidates for federal judgeships.

With her push, Congress formally recognized the office of the first lady as a federal position and provided funding for a staff. Mrs. Carter became the first presidential wife to carry a briefcase daily to a White House office.

While Mr. Carter held himself above politics, saying it was not in his DNA — to the detriment of his presidency, his critics said — his wife acknowledged that for her, politics came naturally.

“I’ve always said I’m more political than Jimmy,” she once said. “I’m political, he’s not.”

Her husband’s advisers concurred. “She is clearly the most political first lady, maybe in history, in terms of being involved in politics and in the campaign,” Patrick Caddell, Mr. Carter’s pollster, told The Times during the 1980 re-election effort.

Robert S. Strauss, former chairman of the Democratic National Committee, called her, admiringly, “a political animal.”

The news media often asked Mrs. Carter whether she should be wielding so much influence given that she had not been elected.

As she told The Times in 1978: “I don’t think the people in this country are worried about where I’m going.” She added: “And I’m not doing what I’m doing for people who write about it. I’m doing it for the people I can help. And I really believe that I can help.”

She pointed out that she had worked outside the home all her life. “I can’t stay at home and do Cokes and teas,” she said, “although I think that for those people who want to do that, then that’s surely important to them.”

The remark was strikingly similar to a sentiment that Mrs. Clinton would express in 1992: “I suppose I could have stayed home, baked cookies and had teas,” Mrs. Clinton said. While Mrs. Clinton’s remark provoked a backlash, Mrs. Carter never drew that kind of wrath; she was not as contentious a figure as Mrs. Clinton and was never perceived as harboring political ambitions of her own.