“It is incredibly important that people within the progressive movement and Democratic Party realize that women are sick of this” stuff, said Erin Matson, a Virginia-based abortion rights activist, “and we’re not going to take it anymore.” (She used a more pungent word than “stuff.”) “What Bernie doesn’t seem to realize,” she added, “is that the abortion rights movement has really bucked up and gotten some tough ovaries in the last couple of years.”

Tom Perez, the party’s newly elected chairman, had been campaigning with Mr. Ossoff in Georgia when Mr. Sanders was in Nebraska. But in interviews leading up to the event, Mr. Perez was unapologetic about supporting Mr. Mello, who has recently said that although he personally opposed abortion, he would uphold abortion rights as mayor.

Yet after the backlash, Mr. Perez retreated. He conducted some quiet diplomacy, telephoning Ms. Hogue and Cecile Richards, the president of Planned Parenthood, according to Democrats briefed on the calls. Casting aside their efforts at unity, Mr. Perez’s aides blamed Mr. Sanders for the event, putting out word that it had been the senator’s idea to include the rally on the tour and criticizing him for not vetting Mr. Mello.

By Friday afternoon, Mr. Perez had issued a far more strongly worded statement. “I fundamentally disagree with Heath Mello’s personal beliefs about women’s reproductive health,” Mr. Perez said. “It is a promising step that Mello now shares the Democratic Party’s position on women’s fundamental rights. Every candidate who runs as a Democrat should do the same because every woman should be able to make her own health choices. Period.”

In an interview on Friday, Mr. Perez further toughened his language, saying he respected those Democrats who “have personal beliefs” against abortion rights but warning them not to pursue such policies in office. “If they try to legislate or govern that way, we will take them on,” he said.

Not every liberal sees the issue as so clear-cut. Ms. Weingarten, who was a Clinton supporter, argued that the question of whether to focus on economic justice or social issues was “not an either-or” proposition. The red-and-blue-state tour that Mr. Sanders and the Democratic National Committee officials are on “conveys to the public that the Democratic Party is first and foremost a party of economic opportunity,” she said.