Acting White House Chief of Staff Mick Mulvaney has been asked to testify in the impeachment inquiry on Nov. 8, according to a letter sent by House Democrats on Tuesday. “Based on evidence gathered in the impeachment inquiry and public reporting, we believe that you posses substantial first-hand knowledge and information relevant to the House’s impeachment inquiry,” reads the letter from the House committees. The lawmakers wrote that the investigation has revealed Mulvaney may have been “directly involved” in President Trump’s plan to withhold a White House meeting and nearly $400 million in aid from Ukraine in exchange for a re-opened investigation into the Bidens, the president’s political foe.

“Your failure or refusal to appear at the deposition, including at the direction or behest of the President, shall constitute further evidence of obstruction of the House’s impeachment inquiry and may be used as an adverse inference against you and the President,” reads the letter. Four senior Trump administration officials failed to show up to scheduled depositions on Monday, citing orders from the White House and an opinion from the Justice Department’s Office of Legal Counsel.