“Mr. Clark’s complete failure to cooperate today is unacceptable,” said Representative Bennie Thompson, Democrat of Mississippi and the chairman of the committee. “As prescribed by the House rules, I have considered Mr. Clark’s claim of privilege and rejected it. He has a very short time to reconsider and cooperate fully. We need the information that he is withholding, and we are willing to take strong measures to hold him accountable.”

Mr. Clark appeared before the committee on Friday but delivered a letter saying he would not answer substantive questions. He cited attorney-client privilege protecting his conversations with Mr. Trump.

“He is duty-bound not to provide testimony to your committee covering information protected by the former president’s assertion of executive privilege,” Mr. Clark’s lawyer, Harry W. MacDougald, wrote in a letter to the committee, which was reported earlier by Politico. “Mr. Clark cannot answer deposition questions at this time.”