• Citing an unpublished manuscript of Bolton's upcoming book, The New York Times reported on Sunday that Bolton claims Trump personally told him last year that he would withhold military aid from Ukraine until it launched a politically motivated investigation into former Vice President Joe Biden.
  • The revelation shatters Trump's biggest defense in the impeachment inquiry: that there are no firsthand witnesses who can directly confirm that he engaged in a quid pro quo regarding Ukraine.
  • It also boxes Republican senators who have been against calling new witnesses in Trump's trial into a corner.
  • Trump disputed Bolton's reported claim, tweeting that he never had any such conversation with the former national security adviser. But Bolton is said to be a meticulous note-taker, which significantly bolsters his credibility as a firsthand witness.
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In the months since Congress launched its impeachment inquiry into President Donald Trump, there was widespread speculation that former national security adviser John Bolton could be Trump's worst nightmare if he decided to testify in the House impeachment hearings or the Senate trial.

This weekend, Bolton proved why.

In a bombshell story, The New York Times reported that in an unpublished manuscript for his upcoming book, Bolton claims Trump personally told him last year that he would withhold military aid to Ukraine until Ukrainian President Volodymyr Zelensky acceded to his demands for politically motivated investigations targeting former Vice President Joe Biden and the Democratic Party.

Specifically, Trump demanded that Zelensky investigate unfounded allegations of corruption against Biden, who is a frontrunner for the 2020 Democratic nomination, and his son, Hunter, related to the younger Biden's employment on the board of the Ukrainian natural-gas company Burisma Holdings. The president also wanted Zelensky to investigate a discredited conspiracy theory suggesting Ukraine interfered in the 2016 election.

The president and his allies have repeatedly claimed his decision to freeze Ukraine's aid had nothing to do with his demands for investigations. Instead, they said, Trump was concerned about European burden-sharing and corruption in Ukraine.

Bolton's revelation "directly contradicts Trump's absurd defense on the facts," Jeffrey Cramer, a longtime former federal prosecutor who spent 12 years at the Justice Department, told Insider. "The Senate can hear the story as part of their responsibilities or they can hear it on Bolton's book tour."

So far, the Republican-controlled Senate has refused to vote on whether to call new witnesses, like Bolton, in the president's impeachment trial. But his revelation about a face-to-face conversation in which the president himself confirmed a quid pro quo security assistance in exchange for a personal, political favor makes it nearly impossible for the GOP to turn a blind eye.

"There is no excuse for not seeking Bolton's testimony," Cramer said. He added that Trump could invoke executive privilege to bar his former national security adviser from appearing before the Senate, in which case it would go to the courts.

Any president can reasonably expect that he can have candid conversations with advisers without the substance of those conversations being publicly revealed. However, Cramer said, executive privilege doesn't extend to potential abuse of power one of the articles of impeachment against Trump and when the evidence is stacked against the president.

Indeed, more than a dozen current and former US officials have testified to Congress, under oath, about Trump's months-long effort to pressure Ukraine to cave to his demands while withholding military aid and dangling a White House meeting Zelensky desperately sought.

The White House also released a summary of the July 25 phone call at the center of the impeachment inquiry, in which Trump repeatedly asked his Ukrainian counterpart to deliver the investigations he wanted. He made the demands immediately after Zelensky indicated Ukraine was ready for more US military aid.

"It would be easier if Trump simply asked for an envelope full of cash," Cramer said. "He didn't need the cash. He needed the announcement of an investigation."

Bolton's reported claim about his conversation with Trump, which he said took place last August, also shatters the key defense the president's lawyers have put forward in his impeachment trial: There are no firsthand witnesses who can testify that Trump himself confirmed a quid pro quo with Ukraine.

"Not a single witness testified that the president himself said that there was any connection between any investigations and security assistance, a presidential meeting or anything else," deputy White House counsel Michael Purpura told the Senate on Saturday.

Bolton's reported claim also adds a significant data point to what Democrats say is an "overwhelming" body of evidence against the president.

Trump, for his part, denied he ever told Bolton he would withhold Ukraine's aid until Zelensky gave in to his demands.

"I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens," the president tweeted. "in fact, he never complained about this at the time of his very public termination. If John Bolton said this, it was only to sell a book."

But it may not be so easy for Trump to write Bolton off.

Not only was he a high-profile figure in Trump's inner circle, but the former national security adviser was also a meticulous note-taker. Bolton is known to create detailed documents of significant meetings and interactions known as contemporaneous memos and such notes are considered admissible evidence in a court of law.

It's not known yet whether enough Republicans will budge on whether to call witnesses in Trump's trial in light of The Times' reporting. But it's clear that at the very least, this throws the Senate proceedings into uncharted territory.

"The odds of deposition for new witnesses is certainly rising dramatically," one senior GOP official told The Washington Post after The Times' story broke.

George Conway, a high-profile conservative lawyer married to White House counselor Kellyanne Conway, also wrote in a Post op-ed that while it was already clear that Trump engaged in a quid pro quo with Ukraine confirmed in testimony from Gordon Sondland, the US's ambassador to the EU Bolton's testimony on the matter "would make that devastating conclusion inescapable, even to Republican senators who have striven mightily to blind themselves to the obvious."

"From Trump on down, they all know how damning Bolton's testimony would be to Trump's defense," Conway, who has frequently been publicly critical of the president, added. "If Bolton testifies to what's in his manuscript, these arguments, weak as they are, will collapse. The words will come from Trump's mouth, because Bolton will have put them there. The direct witness whose absence Trump's lawyers trumpeted will have appeared."

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SEE ALSO: Former national security adviser John Bolton says Trump directly confirmed a Ukraine quid pro quo in a conversation last year