In a crowded Democratic Primary, Mr. Biden is presenting himself as an unapologetic centrist who can build coalitions, and has resisted the idea that the party needs to move far to the left.

“Show me the really left-, left-, left-wingers who beat a Republican,’’ he said before he entered the race. “So the idea that the Democratic Party has kind of stood on its head, I don’t get.”

That stance has left him open to criticism within his party that he is too much a creature of Washington’s past to deal with the urgency of the political moment.

Multiple studies over the years have shown people care about climate change but rarely vote on it. That has made it a low-priority campaign issue — until now. One recent poll conducted in early primary states found that 84 percent of likely Democratic voters ranked acting on climate change as essential or very important. It’s no accident, then, that every 2020 Democratic candidate has cited it as a top priority, even if a majority have yet to announce specific plans.

Julian Brave NoiseCat, director of Green New Deal strategy at Data for Progress, a left-leaning think tank, said he hoped that Mr. Biden’s plan is ultimately a robust one.

“He appeals to white, middle class suburban voters and that’s great, but he’s not doing so well among young people,” Mr. NoiseCat said. “We do have a policy out there designed to build a new climate coalition. It’s called the Green New Deal and he needs to jump aboard it.”

But Paul Bledsoe, a strategic adviser at Progressive Policy Institute and a former Clinton White House climate staff member, praised Mr. Biden for seeking a climate plan that would appeal to working-class Americans. With Congress expected to remain divided no matter who wins the White House, Mr. Bledsoe said developing policies that can actually become law are key.

“Indulging in ideological purity is great until you actually want to solve the problem,” he said.