During his speech in Atlanta, Mr. Biden took pains to state explicitly that he was not repudiating his previous stance on abortion funding and would make “no apologies” for it.

“This is about health care, not politics,’’ a Biden spokesman, TJ Ducklo, said in a statement Friday. “We’re in an unprecedented moment of crisis for choice in this country, and Vice President Biden believes he can no longer support an amendment that blocks access to health care that women need.”

Mr. Biden’s aides believe that he is broadly acceptable with the party’s rank-and-file, no matter what the loudest critics on Twitter may say, but even they concede that he must move on some issues to accommodate where Democrats are today.

Indeed, his reversal on Hyde is the second time his campaign has signaled a preference for caution but quickly realized how difficult that is in this political environment. After an adviser indicated last month that Mr. Biden would seek a “middle ground” on climate change, he was excoriated on the left, prompting him to unveil his green energy proposal earlier this week to demonstrate he is serious about the issue.

Yet even though Mr. Biden is at odds with his party’s liberal wing, he still notches high poll numbers, is poised to raise as much as any of his rivals this quarter and continues to rack up endorsements.

The debate over Mr. Biden’s position on the Hyde Amendment, a Biden adviser said, had been underway inside the campaign for some weeks as his team works on a proposal that aims to expand health care access. Some in the campaign had been arguing that support for the amendment was antithetical to that goal, arguments that intensified on Wednesday and Thursday.



Other supporters of the former vice president, speaking on the condition of anonymity because of the sensitivity of the subject, were frustrated that he shifted on an issue in which polls show most general election voters agree with him. One high-level Biden backer predicted the reversal would be a negative for him in crucial Midwestern states, should he become the nominee.