Lawyers for Donald Trump opted for a high-risk strategy in the sixth day of the president’s impeachment trial on Monday, avoiding mention of a major new development in the case even as Trump tweeted about it and some Republican senators told reporters that the tide against calling witnesses may have shifted.

On Sunday night, news broke that the former national security adviser John Bolton had written a book undermining the central claim of Trump’s defense, that Trump had never conditioned military aid for Ukraine on an announcement of investigations tied to his political rivals.

In fact, Trump told Bolton in a meeting in August that he did not want to send aid until Ukraine delivered material relating to Joe Biden and to supporters of Hillary Clinton, according to sources cited by the New York Times, which first broke the news.

Bolton’s book, to be published in March, spent the day climbing the bestseller list, hitting No 13 as a pre-sale on Amazon. But inside the Senate chamber, the case against Trump had stalled, frozen in time one month ago and impossible, according to the defense, to add to, even as information continued to leak around a plug imposed by Trump.

With a minor exception at the end of the evening, the defense team did not mention Bolton on Monday, while attacking Democrats for failing to present a witness who could offer a first-hand account of Trump’s thinking on the aid and its suspension. The exception came in a monologue by the defense attorney Alan Dershowitz, who said: “Nothing in the Bolton revelations, even if true, would rise to the level of an abuse of power or an impeachable offense.”

“They seem to be operating in a bubble of denial,” said Senator Richard Blumenthal, a Connecticut Democrat, “and I think they are fast losing any shred of credibility by essentially ignoring the evidence, from John Bolton or others.

“They’re saying there isn’t enough evidence, but they’re trying to stop it from coming before the Senate.”

The Bolton bombshell exploded as the impeachment trial nears a crucial juncture, when senators will decide whether to hear from witnesses and collect documents, in a vote that could be taken on Friday.

At least one Republican senator who had not previously called for witnesses, Pat Toomey of Pennsylvania, told colleagues that a one-for-one witness trade might need to be entered with Democrats to answer broad demands for Bolton to testify, the Washington Post reported.

Emerging for a dinner break, Republican senators deflected questions about whether they would support testimony by Bolton.

“We’re going to make that decision on Friday, and not before Friday, regardless of the questions you ask,” said John Barrasso of Wyoming.

“Additional witnesses are not necessary,” said Ted Cruz of Texas, who said he nevertheless wished to call Joe Biden’s son, Hunter, as a witness. “If the Senate later this week … decides to go down the road on additional witnesses, the most important witness for the Senate to hear from is Hunter Biden.”

Trump and his Republican allies wish to avoid testimony by Bolton; the acting chief of staff, Mick Mulvaney; or others, which the defense team appears to believe could damage Trump’s case. However, Democrats and a majority of Americans want witnesses to be called at the trial.

If current or former Trump aides are subpoenaed by the Senate, the White House could go to court to try to prevent their testimony, potentially drawing out the trial, which has had a short run so far compared with historical precedent.

“The average American is saying: ‘Why don’t they want witnesses and documents?’” the Senate minority leader, Chuck Schumer, told reporters. “The overarching question is: if the president did nothing wrong, why is he so afraid of having witnesses and documents?”

Senator Chuck Schumer: ‘The average American is saying, why don’t they want witnesses and documents?’ Photograph: Alex Wong/Getty Images

While they did not dwell on Bolton, those on Trump’s legal team covered significant ground. They advanced a lawyer who worked for Trump during the special counsel Robert Mueller’s investigation to praise Rudy Giuliani’s performance as Trump’s personal lawyer in the Ukraine scheme. They advanced a former Florida attorney general to describe corruption inside the Ukrainian gas company Burisma, which once employed Hunter Biden.

And they advanced Kenneth Starr, the independent counsel whose serial investigations of Bill Clinton culminated in Clinton’s impeachment, to argue that the United States was suffering from a surfeit of impeachment.

“The Senate is being called to sit as the high court of impeachment all too frequently,” said Starr, who bears unique responsibility for the single previous presidential impeachment trial in the last 150 years.

Jay Sekulow, Trump’s personal attorney who has taken the lead in Trump’s defense team, opened the proceedings on Monday with a possible allusion to the Bolton news, declaring that the defense team would not be discussing “non-evidence” that had not been introduced to the proceedings.

Sekulow then reiterated a defense of the president he made in his first day of opening arguments on Saturday.

“Not a single witness testified that the president himself said there was any connection between security assistance and investigations,” Sekulow said.

Trump’s team was expected to continue the president’s defense on Tuesday, after which senators were to have an opportunity to ask written questions over one or two days. A debate on the question of admitting witnesses would follow. A two-thirds majority of voting senators would be required to remove Trump from office.

Trump was impeached last month on charges of abuse of power and obstruction of Congress. He has denied wrongdoing. “The president did absolutely nothing wrong,” the White House counsel, Pat Cipollone, said on Saturday.

Democrats seemed determined to introduce the Bolton allegations at trial at the earliest opportunity, probably during the question period later this week.

Justin Amash of Michigan, a Republican turned independent and a frequent Trump critic, tweeted as the trial continued: “The defense team’s strategy rests on pretending that news doesn’t exist.”