Former White House National Security Adviser John Bolton jolted the debate over Donald Trump's impeachment trial this week, announcing that he's willing to testify. As we discussed yesterday, it created a challenge Senate Republicans would have preferred to avoid: how would they justify excluding voluntary testimony from an important witness with first-hand information about the president's culpability?

At the White House, the anxiety was different, but just as acute: what would Bolton say and how much damage could his testimony do?

Trump addressed the issue yesterday, suggesting Bolton would have very little to offer.

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Q: Will you be okay if John Bolton testifies? He indicated yesterday that he would if he is subpoenaed. TRUMP: Well, that's going to be up to the lawyers. It will be up the Senate. And we'll see how they feel. [Bolton] would know nothing about what we're talking about....

That's a line that might make the president feel better. It's also a line Trump might want senators to believe as they weigh the possibility of witnesses during the upcoming impeachment trial.

It's not, however, even close to being true.

Bolton is a first-hand witness to Trump's Ukraine scheme, participating in a late-August meeting with the president in which Trump was urged to release the military assistance to our vulnerable ally. According to Tim Morrison, the former top National Security Council official for Russia and European affairs, Bolton and Trump also had a one-on-one meeting that month about the aid package that the president delayed.

Bolton's lawyer added in November that the former White House national security adviser was also "part of many relevant meetings and conversations" pertaining to the impeachment investigation that have not yet been made public.

There have also been multiple media reports about Bolton balking behind the scenes at the Ukraine scheme, and according to former White House analyst Fiona Hill, Bolton condemned Trump's political plot as a "drug deal" he didn't want to be caught up in.

It's against this backdrop that Trump argued yesterday that Bolton "would know nothing" relevant to the scandal. There's a whole lot of evidence suggesting otherwise.

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