Acting White House chief of staff Mick Mulvaney on Friday defied a congressional subpoena for his testimony in the House impeachment probe.
Mulvaney did not appear for a closed-door deposition at the Capitol, citing White House claims of immunity, according to an official working on the inquiry.
On Thursday, the House Intelligence Committee subpoenaed Mulvaney for his testimony about his knowledge concerning military aid the Trump administration withheld in order to pressure the Ukrainian government to conduct investigations, including one of the president's political rival, former Vice President Joe Biden and his son, Hunter.
The impeachment official said Mulvaney's outside counsel informed House investigators "one minute" before his scheduled deposition that he would not appear.
"This morning, one minute before his scheduled deposition was to start, Mr. Mulvaney's outside counsel informed us that his client had been directed by the White House not to comply with the duly authorized subpoena and asserted "absolute immunity," the official said in a statement.
President Trump on Friday was asked by reporters on the White House South Lawn why he would not allow his chief of staff to testify before the House committee.
"I don't want to give credibility to a corrupt witch hunt," Trump responded. "I would love to have Mick go up, frankly. I think he would do great. I would love to have almost every person go up when they know me. What I don't like is when they have these people go up that I don't know."
He added: "I have to do what the lawyers say, to a certain extent. But I like to have the people go up. Except one thing. It validates a corrupt investigation."
Democrats said Mulvaney's refusal to testify means the Trump administration is "hiding and trying to conceal the truth from the American people."
"If the White House had evidence to contest those facts, they would allow Mr. Mulvaney to be deposed, as three chiefs of staffs of President Clinton were during his impeachment proceedings," the official added.
ABC News' Katherine Faulders contributed to this report.