The most heated exchange that Mr. Trump had with Ms. Collins was over the special counsel investigation into his possession of hundreds of presidential records, including more than 300 individual classified documents, at his private club, Mar-a-Lago, after he left office.

And it was the area in which he walked himself into the biggest problems.

“I was there and I took what I took and it gets declassified,” said Mr. Trump, who has maintained, despite contradictions from his own former officials, that he had a standing order automatically declassifying documents that left the Oval Office and went to the president’s residence.

“I had every right to do it, I didn’t make a secret of it. You know, the boxes were stationed outside the White House, people were taking pictures of it,” Mr. Trump said, intimating that people were somehow aware that presidential material and classified documents were in them (they were not).

In what will be of great interest to the special counsel, Jack Smith, Mr. Trump would not definitively rule out whether he showed classified material to people, something investigators have queried witnesses about, in particular in connection with a map with sensitive intelligence.

“Not really,” he hedged, adding, “I would have the right to.” At another point he declared, “I have the right to do whatever I want with them.”

He also defended himself for a call he had with Georgia’s secretary of state in which he said he was trying to “find” enough votes to win. “I didn’t ask him to find anything,” Mr. Trump said.

There are few issues that worry the Trump team and the former president as much as the documents investigation, and Mr. Trump wore that on his face and in his words on the stage in New Hampshire.