It prompted one last-minute proposal from Sen. James Lankford (R-Okla.) — backed Tuesday by Sen. Lindsey Graham (R-S.C.) — to obtain and review a copy of the book in a classified setting. Schumer quickly rejected the proposal as "absurd," saying a book should not need to be kept in a secure facility and calling it an effort to deflect from Democrats' demand to call witnesses.

The development also served as a reminder that the case against Trump has unfolded more rapidly than lawmakers can handle, and new evidence could emerge at any moment.

Separately, a top former aide to Ukraine's president Volodymyr Zelensky told The Daily Beast that Ukraine did in fact feel "rattled" by Trump's request that the country investigate his Democratic rivals. That undercut another Trump team defense: That Ukraine did not feel pressured by Trump's call for the probes.

Democrats continued to call for additional witnesses and documents to be brought into the trial and warned that more damaging information about Trump’s interactions with Ukraine could come out.

"In a few weeks or a few months do my Republican colleagues want to pick up the paper and read that one of the witnesses they blocked had crucial information about the president's misconduct?" Senate Democratic leader Chuck Schumer said Tuesday morning. "At this point, how can Senate Republicans not vote for the witnesses and documents we’re seeking?"

The rapidly shifting landscape has left Senate Republicans facing a tricky calculus just as the House’s prosecutors are preparing to retake the stage. The seven House Democrats prosecuting the case will join Trump’s lawyers for a lengthy question-and-answer session with senators, spread over two days.

Senate Majority Leader Mitch McConnell on Tuesday announced he had reached an agreement with Schumer to allow for eight hours of questioning on Wednesday and another eight hours on Thursday. On Friday, after four hours of debate, the Senate will hold a crucial vote on whether to call witnesses.

Jay Sekulow, Trump’s lead personal attorney, again appealed to senators to not consider Bolton’s unpublished book as they decide whether to call witnesses in the Senate’s impeachment trial, saying “[Impeachment] is not a game of leaks and unsourced manuscripts.”

In the 1999 trial of Bill Clinton, senators wrote their questions and submitted them to the chief justice, who then read them aloud. Back then, Republicans and Democrats alternated asking questions and were required to direct their inquiries to either the president's lawyer or the House prosecutors — not both. McConnell said the Trump trial would abide by the same rules.

Trump’s defense spent Monday meandering between philosophical and procedural objections to the House’s charges against him. There was only a limited effort to push back on the facts Democrats presented, and there were presentations in defense of Trump lawyer Rudy Giuliani’s actions in Ukraine, as well as protracted attacks on Joe Biden and Barack Obama.

The White House team’s offensive against Biden appeared to shift the rhetoric of some Senate Republicans. Sen. Joni Ernst of Iowa even questioned whether the former vice president would be damaged by the impeachment proceedings in next week’s Iowa caucuses – a comment that drew a swift rebuke from Biden. In effect, the president’s team used its time Monday to accomplish what Trump sought but never received from Ukraine: a high-profile, politically damaging, innuendo-laden examination of Biden’s handling of Ukraine policy.