Sen. Susan Collins, R-Maine, departs the Senate on Saturday following defense arguments by the Republicans in the impeachment trial of President Donald Trump on charges of abuse of power and obstruction of Congress at the Capitol in Washington. Credit: J. Scott Applewhite | AP

WASHINGTON — Pressure is increasing on senators to call John Bolton to testify at President Donald Trump’s impeachment trial after the revelation that a draft of a book by the former national security adviser undercuts a key defense argument — that Trump never tied military aid to Ukraine to his demand the country help investigate political rival Joe Biden.

Bolton writes in the forthcoming book that Trump told him he wanted to withhold hundreds of millions of dollars in security aid from Ukraine until it helped him with investigations into Biden. Trump’s legal team has repeatedly insisted otherwise, and Trump tweeted on Monday that he never told Bolton such a thing.

Republican senators faced a pivotal moment as they arrived on Capitol Hill to resume Trump’s trial, where the president’s defense lawyers picked up their defense. One, Jay Sekulow, appeared off the bat Monday to take a veiled swipe at the relevancy of the allegations from Bolton in the book draft.

“We deal with transcript evidence, we deal with publicly available information,” Sekulow said. “We do not deal with speculation, allegations that are not based on evidentiary standards at all.”

Democrats are demanding sworn testimony from Bolton and other key witnesses, and pressure is mounting on at least four Republicans to buck GOP leaders and form a bipartisan majority to force the issue.

Four Republicans would have to join Democrats to call any witnesses, which would extend the trial for an undetermined amount of time. Sen. Susan Collins, R-Maine, has said she is likely to support witnesses in a vote that could come likely this week.

Collins said in a Monday statement the reports about Bolton’s book “strengthen the case for witnesses,” adding that it was a topic of conversation among her Senate colleagues. Sen. Mitt Romney, R-Utah, said Bolton’s “relevance to our decision has become increasingly clear.”

The Maine senator said earlier this month that she was working with a “small group of GOP senators” to ensure witnesses were called in the trial. But Collins added that she would only support hearing from witnesses after both the House managers and the president’s legal team present their cases, a position she reiterated on Monday. Collins hasn’t called specifically for Bolton to testify, though she said earlier this month he may be an appropriate witness.

But several Republicans who met privately with Senate Majority Leader Mitch McConnell of Kentucky said nothing had changed. McConnell declined comment while Sen. John Barrasso of Wyoming, the No. 3 Republican, dismissed the information as an “effort to sell books.”

Before any vote on witnesses, Trump’s legal team was to make its case in depth on Monday, turning to several high-profile attorneys to argue against impeachment. The team laid out the broad outlines of its defense in a rare Saturday session, at which they accused House Democrats of using the impeachment case to try to undo the results of the last presidential election and drive Trump from office.

The White House has had Bolton’s manuscript for about a month, and has challenged his use of certain material it considers classified, according to a letter from Bolton’s attorney.

Democrats say Trump’s refusal to allow administration officials to testify in the impeachment proceeding reinforced that the White House is hiding evidence. Senate Democratic leader Chuck Schumer of New York said: “We’re all staring a White House cover-up in the face.”

“I don’t know how you can explain that you wanted a search for the truth in this trial and say you don’t want to hear from a witness who had a direct conversation about the central allegation in the articles of impeachment,” said Rep. Adam Schiff, D-California, who is leading the House prosecution team.

Bolton’s account was first reported by The New York Times and was confirmed to The Associated Press by a person familiar with the manuscript on the condition of anonymity. “The Room Where It Happened; A White House Memoir” is to be released March 17.

Trump denied the claims in a series of tweets early Monday, saying people could look at transcripts of his call with Ukrainian President Volodymyr Zelensky to see there was no pressure for such investigations to get the aid. In that call, Trump asked Zelensky to “do us a favor” with the investigations as he was withholding nearly $400 million in military aid.

“I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens,” Trump said. “If John Bolton said this, it was only to sell a book.”

Trump falsely claimed Monday that the Democrat-controlled House “never even asked John Bolton to testify.” Democrats did ask Bolton to testify, but he didn’t show up for his deposition. They later declined to subpoena Bolton, as they had others, because he threatened to sue, which could lead to a prolonged court battle.

BDN writer Jessica Piper contributed to this report.