LAST WEEK, senators trying the impeachment charges against President Trump did not know for sure whether former national security adviser John Bolton could answer outstanding questions about the case. Now they know. As the New York Times reported on Sunday, the manuscript of Mr. Bolton’s forthcoming book contains a wealth of new information, including an account of the president personally linking aid to Ukraine to his demand for investigations of Democrats. Mr. Bolton has said he will testify if called; if senators now fail to summon him, they will turn the Senate trial into a farce.

Mr. Bolton’s account is particularly important because an integral part of the case Mr. Trump’s lawyers made in their first presentation to the Senate on Saturday was that no direct testimony established Mr. Trump’s motives in freezing military aid to Ukraine. That was already a distortion, since acting White House chief of staff Mick Mulvaney said at a news conference that the president had told him the aid freeze was connected to the politicized investigations he sought. But now, senators know that Mr. Bolton reportedly had a similar conversation — and that it and other original evidence is described in dozens of pages of a book that could appear as soon as mid-March.

According to the Times, Mr. Bolton’s narrative raises questions about other senior officials, including Mr. Mulvaney, Attorney General William P. Barr and Secretary of State Mike Pompeo. Mr. Pompeo reportedly told Mr. Bolton that there was no basis for allegations of wrongdoing against the U.S. ambassador to Ukraine, Marie Yovanovitch, made by Rudolph W. Giuliani, Mr. Trump’s lawyer. Mr. Mulvaney is said to have been present for a phone call in which Mr. Trump and Mr. Giuliani discussed Ms. Yovanovitch. And Mr. Bolton himself reportedly raised concerns with Mr. Barr about Mr. Giuliani’s activities in Ukraine.

Mr. Mulvaney issued a statement Monday denying Mr. Bolton’s account. That should only make it more urgent for senators to summon both men, along with Mr. Barr and Mr. Pompeo, and question them under oath. Otherwise, they will conclude the trial without considering crucial evidence that is, or soon will be, in the public domain. Excuses by Republicans for not doing so are flimsy: for example, that a subpoena of Mr. Bolton would violate the president’s right to shield communications with aides under the doctrine of executive privilege. In fact, since the substance of Mr. Bolton’s account is already public, and it’s unlikely the White House can prevent the publication of his manuscript, the question is moot.

Mr. Trump’s lawyers on Monday chose to ignore the hole Mr. Bolton ripped in their defense. Instead, they offered senators strained or trivial objections to the impeachment procedure the House used, and launched a smear attack against Joe Biden and his son Hunter, despite the absence of any evidence of misconduct in Ukraine. When they addressed the facts of the case, they arrogantly repeated the assertion that “no witness testified” that Mr. Trump made a connection between investigations and military aid. That will only remain true if senators choose to make a mockery of justice by declining to summon Mr. Bolton.

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