A far more representative attitude in the Republican caucus was expressed by Roy Blunt, of Missouri, who said on Monday, “Unless there’s a witness that’s going to change the outcome, I can’t imagine why we’d want to stretch this out for weeks and months.” With this tautology Senator Blunt gives away the game: All witness testimony to date — all presented as part of the House impeachment proceedings — has only strengthened the case against Mr. Trump, but Republicans will not vote to convict him under any circumstances. By definition, then, no witness in the Senate could possibly change the outcome.

The reporting on Mr. Bolton’s manuscript, which is scheduled for publication in March, has scrambled that strategy. Mr. Bolton’s foreign-policy disagreements with Mr. Trump have been public knowledge for months. Last fall, Fiona Hill, a Russia expert and former Bolton aide, testified in the House that Mr. Bolton was alarmed by Mr. Trump’s aid-for-investigations scheme, which Mr. Bolton characterized as a “drug deal.”

In the manuscript, detailed descriptions of which were leaked to The Times, he recounts nearly a dozen instances in which he and other top administration officials pleaded with Mr. Trump to release the aid, to no avail. He describes Mr. Trump’s fixation on conspiracy theories about Ukrainian interference in the 2016 election, and about the supposed corruption of Marie Yovanovitch, the American ambassador to Ukraine. He says that Secretary of State Mike Pompeo admitted privately to him that he knew there was nothing to the theories regarding Ms. Yovanovitch, whom Mr. Trump fired last spring.

Mr. Bolton, a hard-line conservative with decades of service in Republican administrations, is no anti-Trump zealot, which makes his allegations against the president that much more devastating. And his decision to tell these stories publicly nearly certainly waives any claims of executive privilege Mr. Trump might try to assert over their communications.

Let’s not forget the newly revealed evidence that came to light on Saturday, in the form of a tape recording released by the lawyer for Lev Parnas, who had worked for Rudy Giuliani, the president’s personal lawyer, in the Ukraine scheme. Mr. Trump has denied even knowing Mr. Parnas, but on the tape the two men can be heard in conversation at a dinner in April 2018. “Get rid of her,” Mr. Trump said of Ms. Yovanovitch. “Get her out tomorrow. Take her out. O.K.? Do it.”