If the committee members had truly wanted to add to the public’s understanding of the events leading up to the Benghazi attacks, they could have delved into the choices officials at the Department of Defense and the Central Intelligence Agency made before and after the attacks. They could also have examined Congress’s refusal to provide the funding the State Department has requested for security for its overseas installations. Instead, the Benghazi committee has focused only on Mrs. Clinton and her close aides.

“It is a prosecution,” Representative Adam Smith, one of the Democrats on the committee, said during the hearing. “It is a partisan exercise.”

Mrs. Clinton, who lost her temper the last time she testified on Capitol Hill about the Benghazi attacks, was thoughtful and patient on Thursday. She acknowledged the findings of an independent investigation into the attacks led by the former American diplomat Thomas Pickering and retired Adm. Mike Mullen, the former chairman of the Joint Chiefs of Staff. That inquiry identified systemic failings by the State Department, which Mrs. Clinton said she took steps to address before leaving office in 2013.

The suggestion that she was personally negligent and that her team took steps to cover up facts are “a very personally painful accusation,” Mrs. Clinton testified. “I’ve lost more sleep than all of you put together,” she said. “I have been racking my brain about what more could have been done or should have been done.”

Now that the hearing, which was intended to be the climactic point of the Benghazi committee inquiry, is over, the Democrats who reluctantly agreed to join the panel when it was established in May 2014 should walk away. The Republicans are expected to issue a report. May it be the final chapter of a wasteful and counterproductive exercise that accomplished nothing.