“It is you who do all the work and is going to do the responsive work about the shooting of El Paso,” she said. “It’s about the county workers, it’s about state workers, it’s about public service and it’s about first responders.”

Several of the candidates who spoke earlier in the day would go on to deliver emotional appeals for combating gun violence in later statements, including former Vice President Joseph R. Biden Jr., who said he had tried to reach Mr. O’Rourke.

Earlier, he set the tone for the pro-Obama messaging in his AFSCME appearance Saturday morning.

Mr. Biden, who has a habit of going on tangents and fumbling his lines, gave among the most fluent and forceful remarks of his candidacy as he vigorously defended the Affordable Care Act, Mr. Obama’s signature health care law, and advocated for strengthening it, rather than embracing a new system — like, he implied, Medicare for All.

“We should be building on Obamacare, we should not scrap Obamacare,” he said, rising to his feet as he addressed a cheering crowd.

He also defended the Obama administration’s record on health care and immigration, something he would continue to do, fiercely and energetically, throughout two other stops on Saturday, though speaking at AFSCME, he stopped short of accusing his opponents of criticizing Mr. Obama, an argument he had made following the debate. At AFSCME, he said that the administration’s controversial deportation practices focused on “felons.”

[We tracked down the 2020 Democrats and asked them the same set of questions. Watch them answer.]

And he explained his own opposition to decriminalizing illegal border crossings, a view that contrasts with several of his more liberal opponents.

“It will be an invitation to come,” he said of decriminalization, going on to add that he and “Barack” sought to increase “the total amount of immigration” and stressing his support for asylum seekers.