House impeachment investigators would like Mick Mulvaney to tell them more about the quid pro quo involving US aid to Ukraine he talked about during a briefing last month—but the acting White House chief of staff is widely expected to defy a subpoena issued late Thursday. On Oct. 17, Mulvaney "admitted from the White House briefing room that the president withheld vital military aid in order to pressure Ukraine to conduct investigations that would benefit the President’s personal and political interests," an official working on the impeachment inquiry said in a statement, per the Washington Post. Mulvaney "has the opportunity to uphold his oath to the nation and constitution by testifying tomorrow under oath about matters of keen national importance," the official said.
Mulvaney is considered a key figure in the investigation because he was involved in the decision to withhold the military aid, but he is expected to obey a White House directive not to cooperate with House investigators, the Hill reports. Earlier this week, three House committees asked him to testify at a closed-door deposition Friday morning. Politico notes that apart from Mulvaney's "jaw-dropping" remarks, which he later walked back, there has been no official explanation for the hold on military aid, which came as Rudy Giuliani and others were urging Ukraine's government to investigate the Bidens. The official working on the inquiry said investigators hope Mulvaney won't hide behind Trump's "ongoing efforts to conceal the truth and obstruct our investigation." (Read more Trump impeachment stories.)