President Donald Trump’s lawyers avoided the explosive allegation in former National Security Advisor John Bolton’s book that the president tied aid to Ukraine to an investigation of a political rival as they sought to undermine the House impeachment case.

Trump’s attorneys continued to rely heavily Monday on the lack of firsthand evidence in the House argument that Trump held up release of military aid for Ukraine to pressure its government for help to tarnish former Vice President Joe Biden, a potential challenger to the president in November. They urged senators to block Democratic efforts to seek new witness testimony at the Senate trial.

In the manuscript of his book, Bolton wrote that in August the president told him he didn’t want to send US$391 million in security assistance to Ukraine until the government there turned over material related to Biden, according to the New York Times, citing unnamed people who had seen the draft.

“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 at all,” Trump attorney Jay Sekulow said.

Two key GOP senators, Susan Collins and Mitt Romney, said the leak about Bolton’s unpublished manuscript has prompted new discussions among Republicans about subpoenaing witnesses. Trump ally Lindsey Graham told a Washington Post reporter he wants the White House to give senators a copy of Bolton’s book manuscript to determine whether Bolton should be called.

Trump’s lawyers, meanwhile, made a sober, subdued defense dismissing the House’s charges as full of holes, legally deficient and based on a flawed, partisan process in the House with limited opportunities for the president to defend himself.

Patrick Philbin made the argument -- echoed by GOP leaders -- that the Senate should not add to the evidence collected by the House, lest that become the new norm for presidents. And he warned that it was “absurd” and “dangerous” for the House to charge Trump with obstructing Congress when he relied on opinions from the Department of Justice that he did not need to comply with subpoenas.

Philbin said the House could have contested its subpoenas in court but declined to do so. House managers have said they didn’t have time to wait on the courts to protect the integrity of the November election for the White House and Congress.

Trump’s defense also sought to argue that Trump was justified in wanting to probe possible corruption in the appointment of Biden’s son, Hunter Biden, to the board of Burisma Holdings, a Ukrainian energy company that had been embroiled in controversy.

“All we are saying is that there was a basis to talk about this, to raise this issue, and that is enough,” Trump lawyer Pam Bondi said.

Potential Delays

The Bolton revelation has revived talk among Trump’s defenders, including Graham and Josh Hawley, of calling witnesses who Trump wants to testify. Hawley has prepared a series of motions to subpoena testimony and documents from Adam Schiff, the House Intelligence chairman who led the impeachment inquiry; the still-anonymous intelligence community whistle-blower; and Biden and his son, who was on the board of a Ukrainian energy company.

A long lineup of witnesses threatens to extend the trial by weeks or months, and it’s not clear there are 51 Republican votes to bring in either Biden.

Democrats Monday morning said the revelations bolster their case for witnesses and reiterated their demand for a subpoena for acting Chief of Staff Mick Mulvaney as well. He was in the middle of the decisions on Ukraine aid and publicly stated it was withheld in part because of a desire for Ukraine to launch an investigation into a discredited theory that Ukraine rather than Russia was involved in election interference in 2016.

Bolton wrote that Mulvaney was among several top cabinet officials who had knowledge of Trump’s demands. A lawyer for the acting chief of staff said he denies Bolton’s assertion.

Romney said Monday he has been talking to other senators and believes it is now “increasingly likely” that there will be enough Republicans to call Bolton to testify.

‘Weeks and Months’

GOP leaders were still trying to keep a lid on new evidence heading into lunch Monday.

“Unless there’s a witness who’s going to change the outcome, I can’t imagine why we’d want to stretch this out for weeks and months,” Missouri Republican Senator Roy Blunt, a member of Majority Leader Mitch McConnell’s leadership team, said. “And if we call any witnesses who are subject to privilege, it would take weeks and months.”

John Thune, the No. 2 Senate Republican, said his colleagues would talk about what to do and suggested “people just kind of stay calm here” and see how Trump’s defense handles the Bolton revelations.

“You sort of suspect that stuff like this is going to happen in this environment,” he said. “But yeah, I mean, it’s a little surprising.”

The debate over witnesses caused rifts within the Senate’s Republican majority. Georgia’s Kelly Loeffler, who was recently appointed to fill an open seat, said on Twitter that Romney “wants to appease the left by calling witnesses who will slander the @realDonaldTrump during their 15 minutes of fame.”

‘Age of Impeachment’

In an ironic twist, Trump’s defense turned to Bill Clinton’s prosecutor Kenneth Starr to complain that impeachments are becoming too common.

“We are living in what I think can aptly be described as the age of impeachment,” said Starr, who investigated Clinton for years as independent counsel.

Starr said that after the Clinton impeachment both parties decided “enough was enough” and allowed the independent counsel statute allowed to expire.

But, he said, “the impeachment habit proved to be hard to kick.”

Trump’s defenders have about 22 hours under the rules to put on their case today and tomorrow, followed by 16 hours of senators’ questions likely to last another two days.

That sets up Friday as the likely key day for voting on whether to consider motions calling witnesses or subpoenaing documents. If successful, senators could offer and debate motions on witnesses. If Republican leaders succeed in blocking new evidence, the Senate would move quickly to a final vote where senators would vote “guilty” or “not guilty” on the two charges against Trump -- abuse of power and obstruction of Congress.