President Donald Trump’s defense lawyers wrapped up their argument Tuesday that his actions on Ukraine don’t warrant removal from office, while senators focused on building pressure to call former National Security Advisor John Bolton to testify.

“I think we’ve made our case,” White House Counsel Pat Cipollone said as he delivered his final presentation. “The articles of impeachment fall far short of any constitutional standard and they are dangerous.”

The president’s team has accused Democrats of pursuing a partisan impeachment, arguing that there was no direct link between Trump’s decision to withhold financial aid from Ukraine and his pressure on that country to investigate political rival Joe Biden.

Bolton said the opposite, though, according to the New York Times, which reported that his forthcoming book says Trump directly linked the release of aid for Ukraine to investigations of Biden.

While some Republicans are insisting the Bolton report adds nothing new, Senators Susan Collins and Mitt Romney among others have said the leaked account spurred new talks among Republicans about allowing witnesses. Democrats argue that a trial without testimony from Bolton would be a sham.

“I think Bolton probably has something to offer us,” said Alaska Republican Lisa Murkowski, who is viewed as a barometer of whether there will be enough Republican votes to call witnesses. “We’ll figure out how we’re going to learn more.”

The Senate likely will be asked to decide that crucial question later this week, after 16 hours of senators’ questions to each side’s lawyers on Wednesday and Thursday.

A decision to call Bolton or any other top Trump administration official is likely to spur a fight with the administration over executive privilege.

Some Republican lawmakers have said they’ll seek testimony from Biden’s son, Hunter, if Bolton or other witnesses are called.

Trump attorney Jay Sekulow told senators Tuesday to ignore the leaks about Bolton’s book.

Impeachment “is not a game of leaks and unsourced manuscripts. That’s politics unfortunately, and Hamilton put impeachment in the hands of this body, the Senate, precisely and specifically to be above that fray,” he said.

“You cannot impeach a president on an unsourced allegation,” he said.

Two Republicans, James Lankford and Lindsey Graham, suggested senators review Bolton’s manuscript in secret ahead of the crucial vote Friday on whether to call witnesses. But Sekulow called the manuscript “inadmissible.”