Many in the Democratic primary field have heightened their denunciations of Mr. Trump, labeling him a racist and a white supremacist.

As he left the White House for a vacation at his New Jersey golf club on Friday night, Mr. Trump called for lawmakers to pass “meaningful” background checks, a sign that the president finds himself under new political pressure.

Even so, there were no major signals on Friday from the N.R.A., the White House or Capitol Hill that action on the politically fraught issue was closer to compromise or resolution.

Setting himself apart from his rivals, former Representative Beto O’Rourke stayed home in El Paso to attend memorials and visit with shooting victims in his mourning hometown.

“I’m here to make sure that at this moment we do not allow ourselves to be defined by this act of terror,” he said, by way of a video message, “but instead by the way this community overcomes this attack.”

Outside, young boosters for a half-dozen campaigns chanted and screamed at each other. Someone played “Come on Eileen” for no discernible reason. And former Vice President Joseph R. Biden Jr. slow jogged outside to greet his supporters.

The speeches at the Wing Ding dinner surpassed the two-hour mark, with 22 candidates each delivering their pitch in back-to-back-to-back five-minute increments to a sweaty room of Democratic activists. Several opened their comments with cracks about the size of the field, a reality that’s begun to worry party officials and voters.