Ever since leaks from former National Security Adviser John Bolton's forthcoming book made their way to the public, the odds of the Senate calling him as a witness to take the stand in President Trump's impeachment trial appear to have gone up. Speculation about other witnesses has also entered the fold. One of those potential witnesses is acting White House Chief of Staff Mick Mulvaney, who famously admitted to Trump's Ukraine quid pro quo during a press conference last year.

But through his lawyer, Mulvaney denied knowing anything about the revelations in Bolton's books or ever having a conversation with Trump about freezing Ukrainian military aid in exchange for announcing investigations into Trump's domestic political opponents.

At first glance, it seems like Mulvaney and his counsel are taking a proactive approach should the Senate issue a subpoena, as well as launching an effort to discredit Bolton. But CNN's Jake Tapper pointed out that Bolton may not have alerted Mulvaney to his concerns about the Trump administration's Ukraine policy because he reportedly thought Mulvaney played a central role in its formation. Tim O'Donnell