Transcript for John Bolton book manuscript upends impeachment hearings
But we move on to the other news tonight, and to that bombshell report involving John Bolton and president trump. Will it upend the 'em peachment will it lead to witnesses? "The New York Times" reporting on the draft of the book, and Bolton says that the president told him withholding aid was died to Ukraine's investigations. What senators are now saying about possible witnesses about the trial tonight. Mary Bruce on the hill again tonight. Sir, how are you doing today? Reporter: The president's former national security adviser, John Bolton, smiling and waving to cameras this morning after upending the impeachment proceedings. Do you have any evidence of your claims, sir? Reporter: According to "The New York Times," Bolton writes in his upcoming book that president trump personally told him he wanted to continue freezing nearly $400 million in security aid until Ukraine helped to investigate his rivals, including Joe Biden. It directly contradicts what the president's defense team has been arguing. There was no connection between security assistance and investigations. Reporter: The president's lawyers today never once mentioning Bolton. But the president tweeting, "I never told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens. If John Bolton said this, it was only to sell a book." Does this increase the chances you could be called to testify? Well, I haven't seen a manuscript, but I can tell you, nothing was ever said to John Bolton. Reporter: Bolton's reported first-hand account sending a seismic shock through capitol hill where senators will have to decide whether to allow him as a witness. It's pretty fair to say that John Bolton has a relevant testimony to provide to those of us who are sitting in impartial justice. Reporter: Senator Mitt Romney says it's increasingly likely that other Republicans will join him. The reporting on John Bolton strengthens the case for witnesses. Reporter: But the president's lawyers argue senators should focus on the evidence from the house investigation and nothing more. We deal with transcript evidence. We deal with publicly available information. We do not deal with speculation. And Mary, you're learning tonight they're now preparing for the possibility of a trial with witnesses, the president's team? Reporter: David, sources tell us that tonight, the president's team is preparing for the very real possibility that Bolton may be called to testify and they are ready to fight it in court. David? All right, Mary Bruce tonight. Mary, thank you.
This transcript has been automatically generated and may not be 100% accurate.