WASHINGTON (AP) — Former White House counsel Pat Cipollone arrived Friday on Capitol Hill for a private interview with the Jan. 6 committee about his role in trying to prevent then-President Donald Trump from challenging the 2020 presidential election and joining the violent mob that laid siege to the Capitol.

Cipollone had been a sought-after witness after bombshell testimony revealed his apparently desperate and last-ditch efforts to prevent Trump’s actions. The panel was told he warned the defeated president would be charged with “every crime imaginable” if he went to the Capitol on Jan. 6, 2021, trying to stop the certification of Joe Biden’s election. Cipollone was subpoenaed for his testimony.

But the conservative attorney, once a staunch presidential confidant who had defended Trump during his first impeachment trial, had been reluctant to appear formally for an on-record interview. Like other former White House officials, he could claim his counsel to the Republican president is privileged information he is unwilling to share.

The panel said Cipollone is “uniquely positioned to testify” in a letter accompanying the subpoena issued last week.

“Mr. Cipollone repeatedly raised legal and other concerns about President Trump’s activities on January 6th and in the days that preceded,” Chairman Bennie Thompson, D-Miss., said in a statement. “While the Select Committee appreciates Mr. Cipollone’s earlier informal engagement with our investigation, the committee needs to hear from him on the record, as other former White House counsels have done in other congressional investigations.”

Cipollone’s central role came into focus during a surprise committee hearing last week when former White House aide Cassidy Hutchinson described his repeated efforts to stop Trump from joining the mob at the Capitol.

Hutchinson said Cipollone urged her to persuade her boss, chief of staff Mark Meadows, not to let Trump go to the Capitol.

Hutchinson testified that she was told Trump was irate when he was ultimately prevented by his security team from going to the Capitol that day. The Secret Service has disputed parts of her account detailing Trump’s actions when she said he lashed out at the driver in the presidential motorcade.

Cipollone was also part of a key meeting on the Sunday before the Jan. 6 attack with Justice Department officials at the White House threatening to resign if Trump went ahead with plans to install a new acting attorney general who would pursue his false claims of voter fraud.

Cipollone and his lawyer, Michael Purpura, who also worked at the Trump White House, did not respond to requests for comment.

Earlier this week, Trump responded to news of Cipollone’s cooperation on his social media platform, Truth Social, calling it bad for the country.

“Why would a future President of the United States want to have candid and important conversations with his White House Counsel if he thought there was even a small chance that this person, essentially acting as a “lawyer” for the Country, may someday be brought before a partisan and openly hostile Committee in Congress,” the former president said.

Associated Press writer Jill Colvin in New York contributed to this report.