Ms. Pelosi’s staff watched the video together and later recounted how the sounds of the attack stay with them: the screams in the Rotunda and the force with which the rioters beat on the door…

Seated in the chamber, several senators appeared visibly distressed: There were sharp intakes of breath during footage of rioters cursing Ms. Pelosi, tightened fingers on armrests and, in the case of Mr. Schumer, a slow nodding of the head as he watched himself flee the mob. Several senators left for a dinner recess with red eyes, visibly emotional and avoiding questions.

Senator Brian Schatz, Democrat of Hawaii, called the video evidence “gut-wrenching.”

“The historical weight of the insurrection resonated today for a lot of members,” Mr. Schatz said. “Frankly, I think there were some colleagues on the other side of the aisle that hadn’t quite grasped the threat that we were under, physically, and the real peril for American democracy. Whether that moves any votes, I have no idea. But you could feel the weight in the air, and you feel the emotion in the room.”