WASHINGTON ― The bombshell revelation that former national security adviser John Bolton has written a book essentially confirming the Democrats’ case against President Donald Trump went curiously unaddressed by the president’s lawyers on Monday in the Senate impeachment trial.

Bolton’s book alleges that Trump tied the release of congressionally approved Ukraine aid to the Ukrainians’ announcing investigations of former Vice President Joe Biden and his son Hunter Biden, The New York Times reported on Sunday. The report caught Senate Republicans by surprise and upped the pressure for them to allow witnesses ― Bolton included ― to be heard and other evidence to be presented in the trial.

Following the Times story, Sen. Mitt Romney (R-Utah) said it was “increasingly likely” that at least four Republicans would join Democratic senators in passing a motion to subpoena Bolton.

But Trump’s lawyers conspicuously avoided referring to Bolton during Monday’s arguments. Instead, they kept insisting there was no connection between the security assistance to Ukraine and any investigation desired by Trump, contrary to Bolton’s reported account and the testimony of more than a dozen diplomats last fall.

“We deal with transcript evidence. We deal with publicly available information. We do not deal with speculation, allegations that are not based on evidentiary standards,” said Jay Sekulow, one of Trump’s personal attorneys, in a brief allusion to the Times story.

Only Harvard Law School professor Alan Dershowitz, a member of Trump’s defense team, referred to the Bolton allegations, albeit in passing. He did so late in the evening in the middle of a one-hour lecture on why abuse of power isn’t an impeachable offense ― a theory contradicted by many experts, including Attorney General William Barr.

“Nothing in the Bolton revelations, even if true, would rise to the level of an abuse of power or an impeachable offense. That is clear from the history, that is clear from the language of the Constitution — you cannot turn conduct that is not impeachable into impeachable conduct simply by using words like ‘quid pro quo’ and ‘personal benefit,’” Dershowitz said.

In his remarks before the Senate, White House deputy counsel Mike Purpura said that nobody testified “in House records” that Trump had linked the aid to Ukraine with investigations of the Bidens or with a White House meeting between Trump and Ukranian President Volodymyr Zelensky.

That’s not true. Gordon Sondland, the U.S. ambassador to the European Union, testified in the House impeachment inquiry last year that, based on his conversations with the president, it was his understanding that the Ukraine aid was linked to investigations of the Bidens and that “everyone was in the loop.” Trump’s defenders have argued that Sondland’s statements were based merely on his own assumptions.

The House asked Bolton to testify in October, but he did not appear because the White House did not authorize him to do so. House Democrats decided not to pursue the matter in court, arguing that doing so would have taken months of legal action.

Now, Senate Democrats want to hear from witnesses like Bolton and acting White House chief of staff Mick Mulvaney, who as firsthand witnesses could shed more light on the Ukraine aid delay. The 45 Democratic senators and two Democratic-leaning independents need four Republican senators to vote with them to support motions to subpoena witnesses and other evidence.

Republicans, meanwhile, sought to dismiss the Bolton development and its potential impact on the length and scope of the trial.

“Truly, there’s nothing new here. It does seem to be an effort to sell books,” Sen. John Barrasso (R-Wyo.) told reporters on Monday, suggesting Bolton’s credibility was at issue.

“Right now I don’t see any need to have more witnesses, unless we have a lot more witnesses,” Sen. Kevin Cramer (R-N.D.) said. “I don’t think it’s appropriate to use the U.S. Senate as a fishing hole.”

“My view is witnesses would just be prolonging the same outcome,” Cramer said. “I’m not so naive as to think the Bolton revelation didn’t cause some people some pause, but I don’t know what any individual is thinking one way or the other.”

The president’s defense team argued that Trump did nothing wrong during that July 25 phone call last year when he asked Zelensky to investigate Trump’s domestic political opponent.

“Asking a foreign leader to get to the bottom of issues of corruption is not a violation of an oath,” Sekulow said.

In the phone call, the president specifically asked for an investigation of the Bidens and did not mention any general concerns about corruption. But Trump’s attorneys described Hunter Biden as a one-man whirlwind of corruption for his role on the board of Burisma, a Ukrainian energy company, while his father oversaw Ukraine policy as vice president of the United States.

“Every witness who was asked about Hunter Biden’s involvement at Burisma agreed there was a potential appearance of a conflict of interest,” former Florida attorney general Pam Bondi said Monday, describing House testimony.

However, Kurt Volker, the former U.S. special envoy for Ukraine, testified in the House inquiry that he saw no validity to Trump’s allegations against the Bidens. Other diplomats said pushing an investigation of the Bidens benefited Trump, not the U.S. national interest.

Bondi said Democrats themselves had brought up the Bidens, and she frequently referred to media reports questioning Hunter Biden’s board seat, including a Washington Post story in which a controversial former Ukrainian prosecutor claimed that Joe Biden had urged the prosecutor’s firing because he’d been investigating Burisma. (In fact, the prosecutor was widely accused of being insufficiently aggressive in pursuing corruption.)

“All we’re saying is there was a basis to raise this, to talk about this issue, and that is enough,” Bondi said.

In the House impeachment articles, Democrats allege that Trump withheld military assistance, as well as a coveted White House visit, in order to get Zelensky to announce the investigations Trump wanted. Because Ukraine ultimately received the security assistance that had been withheld, and because Trump ultimately did meet with Zelensky, Trump’s lawyers insisted on Monday that no harm was done.

Trump and Zelensky met in New York on Sept. 25, “all without anyone making any statement about any investigations,” Purpura said. “So much for quid pro quo for a meeting with the president.”

Zelensky never got the White House visit he wanted, however. At their New York meeting, he thanked Trump for an invitation but seemed to complain that he’d been left hanging.

“You invited me,” Zelensky said. “But I think — I’m sorry, but I think you forgot to tell me the date.”

Ryan J. Reilly contributed reporting.