“You’ve never heard me say ‘middle of the road,’ I’ve never been middle of the road on the environment,” Mr. Biden said when asked to respond to comments Ms. Ocasio-Cortez issued the night before. “And, tell her to check, you know, the statement that I made and look at my record, she’ll find that nobody has been more consistent about taking on the environment and the green revolution than I have.”

Those remarks came in response to a reporter who read aloud some of Ms. Ocasio-Cortez’s comments, which she made Monday night at a rally in support of a sweeping environmental proposal known as the Green New Deal.

After listing a series of past abuses related to the environment, Ms. Ocasio-Cortez issued what was widely interpreted as an indictment of Mr. Biden. “I will be damned if the same politicians who refused to act then are going to try to come back today and say we need a middle-of-the-road approach to save our lives,” she said. “That is too much for me.”

In style and on many policy issues, Mr. Biden is campaigning as a centrist in a sprawling field that features a number of candidates from the progressive left, who are advocating substantive change. He said recently that he did not believe the Democratic electorate had moved as far left as many in the party assume.

During his New Hampshire swing this week, Mr. Biden pledged to release more details on his environmental proposals by the end of the month, and detailed his record on combating climate change dating to the 1980s. He also spent time, both in conversations with reporters and unprompted on the stump, casting himself as a longtime champion of the environment and defending his record on climate change, a key issue to many progressive voters.