As President Donald Trump’s lawyers continued their defense Monday, Connecticut Sens. Richard Blumenthal and Chris Murphy joined other Democratic colleagues in saying new revelations from John Bolton bolsters their case for summoning witnesses in the Senate’s impeachment trial.

“We need to hear from (Bolton) and see his manuscripts and his notes,” Blumenthal said.

In his forthcoming book, former national security adviser Bolton alleges Trump directly tied the holdup of nearly $400 million in U.S. military aid to Ukraine’s investigation of former Vice President Joe Biden and his son Hunter. The New York Times broke the story Sunday.

The allegation – which is at the heart of the charges against the president— prompted two Republican senators, Sue Collins of Maine and Mitt Romney of Utah, to consider supporting Democrats who want to call Bolton and others as witnesses in the Senate trial.

But four Republicans must vote with the Democrats for a motion to succeed that calls in witnesses and/or solicits new documents.

“My Republican colleagues are seemingly silent on the Bolton issue,” Blumenthal said during a break in the trial. “Aside from vague noises about ‘maybe witnesses’ and ‘maybe documents.’”

Murphy said he did not know if his GOP colleagues would “step up to the plate,” and vote to allow for witnesses and documents.

He said his conversations with Republican senators “have been harder and harder,” after the impeachment trial got underway.

Murphy also said Bolton’s allegations do not come as a surprise.

“We have voluminous testimony from dozens of witnesses and conspirators about this scheme,” he said.

Blumenthal said if Republicans “made a decision now,” in the second week of Trump’s trial, witnesses could immediately be deposed behind closed doors.

Republicans argue that House impeachment investigators should have called in the witnesses Senate Democrats want to hear from – and battle the White House in court if it continues to block them.

Republicans are also advancing another argument – that the White House would claim executive privilege and block witnesses, resulting in months-long delays in the trial as the courts consider the conflict between Congress and the executive branch.

At the end of the day, however, roiled by Bolton’s allegations, some Republican senators floated the idea of a one-for-one exchange of witnesses, Bolton for Hunter Biden.

Meanwhile, Trump on Monday denied speaking with Bolton about any quid pro quo.

In the 1999 impeachment trial of former President Bill Clinton, the Senate voted to hear from witnesses and spent five days taking depositions. Those depositions were taken after opening arguments and after senators submitted questions to the House impeachment managers and Clinton’s defense team.

The defense of the president on Monday was kicked off by former independent counsel Ken Starr, who investigated Clinton. Starr slammed House Democrats, saying they had denied Trump “basic rights” during the House impeachment inquiry by blocking the participation of the president’s lawyers, although the House Judiciary Committee had invited them to participate.

Starr also lamented the United States is now in the “age of impeachment,” and argued the two articles of impeachment approved by the House — abuse of power and contempt of Congress — are not impeachable offenses because they are not crimes.

“All the (legal) scholars reject the argument that it must be a crime,” Blumenthal said.

He also said Starr’s argument “gave new meaning to the word ‘irony,’ or maybe ‘hypocrisy.’”

Starr vigorously pursued Clinton’s impeachment on the charge that he lied to investigators about sex with White House intern Monica Lewinsky.

Late in the day,  Harvard Law School professor  a and member of Trump defense team, Alan Dershowitz, also said he could not find constitutional justification for the impeachment of a president for non-criminal conduct, or conduct that was not at least “akin” to defined criminal conduct.

Before Dershowitz made his case, the  president’s lawyers focused on the Bidens.

Pam Bondi questioned why Hunter Biden was given a seat on the board of Ukrainian gas company Burisma, unless it was “because his last name was Biden.”

Trump’s legal team say the president had every right to ask Ukraine to investigate “corruption” because of  Hunter Biden’s involvement in Burisma.

Blumenthal called this legal tactic “a losing argument” because, he said, there’s no evidence the Bidens did anything wrong.

Blumenthal also said Trump’s lawyers were  operating within a “bubble of denial,” because none of them mentioned Bolton on Monday.

“The rest of America is talking about John Bolton and not a single mention of him in this chamber,” Blumenthal said.