The committees asked the Justice Department to allow former officials to testify after they opened investigations this year into the Trump White House’s efforts to undermine Mr. Biden’s victory, a pressure campaign that occurred in the weeks before Mr. Trump’s supporters attacked the Capitol as Congress met to certify the electoral results.

The Justice Department and the White House Counsel’s Office generally deny such requests because they believe deliberative conversations between administration officials should be protected from public scrutiny.

But they ultimately decided to allow the interviews to proceed, saying in letters to the potential witnesses that the scope of the investigation concerned “extraordinary events,” including whether Mr. Trump tried to improperly use the Justice Department to advance his “personal political interests,” and thus constituted “exceptional circumstances.”

In his letter, which was reported earlier by Politico, Mr. Collins also said Mr. Trump continued to believe that the information sought by the committees “is and should be protected from disclosure by executive privilege.”

Mr. Collins said that no president had the power to unilaterally waive that privilege, and that the Biden administration had “not sought or considered” Mr. Trump’s views in deciding not to invoke it.

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