Speaker Nancy Pelosi also accused Mr. Barr of committing a crime by lying to Congress at a hearing in April, when he said he was unaware of objections from the special counsel to a summary of the report. Mr. Mueller wrote to him about the summary in March. A Justice Department spokeswoman called Ms. Pelosi’s comments “reckless, irresponsible and false.”

What’s next: Democrats could begin contempt proceedings as soon as next week, although the process would probably take months to play out. They also want Mr. Mueller to appear for a hearing.

Partisan picks: Writers from across the political spectrum discuss Mr. Barr’s Senate testimony.

Another angle: The F.B.I. sent an undercover investigator to meet with a Trump campaign aide, George Papadopoulos, in 2016. It was part of a counterintelligence inquiry that has become a political flash point, as President Trump and his allies have accused American law enforcement and intelligence officials of spying on his campaign.