The decision on Thursday not to file criminal charges against President Biden for mishandling classified documents should have been an unequivocal legal exoneration.

Instead, it was a political disaster.

The investigation into Mr. Biden’s handling of the documents after being vice president concluded that he was a “well-meaning, elderly man with a poor memory” and had “diminished faculties in advancing age” — such startling assertions that they prompted a fiery and emotional attempt at political damage control from the president within hours.

Speaking to the cameras from the Diplomatic Reception Room at the White House, Mr. Biden on Thursday evening blasted the report by Robert K. Hur, the special counsel, accusing the report’s authors of “extraneous commentary” about his age and mental capacity.

“They don’t know what they’re talking about,” the president said flatly.

Mr. Biden appeared to take special exception to the report’s assertion that during interviews with F.B.I. investigators, he could not recall what year his son Beau died.

“How the hell dare he raise that,” the president said, appearing to choke back tears. “Every Memorial Day we hold a service remembering him attended by friends and family and the people who loved him. I don’t need anyone, I don’t need anyone to remind me when he passed away.”