There may be enough new pressure on Senate Republicans to allow witnesses at President Trump's impeachment trial, after the leak from a forthcoming book by former national security adviser John Bolton that contradicts what the White House has been telling the country.

Why it matters: This is a dramatic, 11th-hour inflection point for the trial, with an eyewitness rebuttal to Trump's claim that he never tied the hold-up of Ukrainian aid to investigations into Joe Biden.

• GOP sources say the revelation could be enough to sway the four Republican senators needed for witnesses — especially since Sens. Mitt Romney of Utah and Susan Collins of Maine have already strongly signaled they’d vote for witnesses.

What happened: Bolton alleges in his book — "The Room Where It Happened," out March 17 — that Trump explicitly told him "he wanted to continue freezing $391 million in security assistance to Ukraine until officials there helped with investigations into Democrats including the Bidens," the N.Y. Times reported.

• Trump strongly denied Bolton's claims on Twitter early today: "I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens. ... If John Bolton said this, it was only to sell a book."

The state of play: Republican sources tell Axios that party leaders and the White House will still try to resist witnesses because, as one top aide put it, "there is a sense in the Senate that if one witness is allowed, the floodgates are open."

• "If [Bolton] says stuff that implicates, say Mick [Mulvaney] or [Mike] Pompeo, then calls for them will intensify," the aide said.

What we can expect Trump's defense lawyers to say as they make their case at the trial, beginning at 1 p.m. today and continuing tomorrow:

• They'll say Bolton's account doesn’t change any key facts, and reiterate that the aid, which was only briefly paused, was released without the announcement of any investigations.

• They'll emphasize that Ukrainian President Volodymyr Zelensky said there was no pressure, the call record shows no linkage between the two, and Zelensky got his meeting with Trump at the UN.

• They'll also argue that Trump’s concerns about corruption in Ukraine were well-known: He questioned giving aid to the country for a number of reasons, just as he has done with other countries.

The intrigue: Bolton submitted the book to the White House on Dec. 30 for a standard prepublication security review for classified information.

• The Times notes: "The submission ... may have given Mr. Trump’s aides and lawyers direct insight into what Mr. Bolton would say if he were called to testify."

• "It also intensified concerns among some of his advisers that they needed to block Mr. Bolton from testifying."

Between the lines: Trump's defense team has the advantage of being able to do triage at the trial for the next two days, while the House managers listen silently.

• So Dems are making a public case, with Senate Minority Leader Chuck Schumer tweeting: "John Bolton has the evidence."

https://www.axios.com/john-bolton-testimony-trump-impeachment-trial-853e86b0-cc70-4ac6-9e5f-a8da07e7ac93.html