In 2020, Mr. Biden won the national vote by 4.4 percentage points, but barely squeaked out wins by less than one percentage point in Georgia, Arizona and Wisconsin. To win, he needed one of the three.

In 2020, Mr. Biden won the national vote by 4.4 percentage points, but barely squeaked out wins by less than one percentage point in Georgia, Arizona and Wisconsin. To win, he needed one of the three.

The final possibility is that the conditions may be in place for Mr. Biden’s ratings to rebound. It would not be the first time: Ronald Reagan, Bill Clinton, Barack Obama and even Mr. Trump (before coronavirus) saw their approval ratings increase from the low 40s in the two years before re-election. In this scenario, Mr. Biden’s ratings would increase as a crucial segment of voters judged him against the alternatives, rather than in isolation. His re-election campaign would offer a more forceful and energetic defense of his performance, perhaps against the backdrop of low unemployment and fading inflation.

Historically, the third possibility seems more likely. Mr. Biden’s age shouldn’t be understated as a legitimate factor, but he won despite his age last time, and incumbent presidents usually win re-election. The large number of voters who dislike Mr. Trump and once liked Mr. Biden create upside. The direction of the economy will be a crucial variable, of course, but at least for now the combination of low unemployment and slowly fading inflation would seem to provide enough ammunition for Mr. Biden to make his case. Still, his ratings are low enough today that they could improve markedly without securing his re-election.

Three kinds of voters appear to loom large as Mr. Biden tries to reassemble the coalition that brought him to the White House in 2020: young voters, nonwhite voters and perhaps low-income voters as well. In the most recent surveys, Mr. Biden is badly underperforming among these groups. Overall, he could be running at least a net 10 points behind what he earned in 2020 among each of these groups, helping to explain why the early general election polls show a close race.

Mr. Biden has shown weakness among all of these groups at various times before, so it is not necessarily surprising that he’s struggling among them again with his approval rating in the low 40s. Still, they crystallize the various challenges ahead of his campaign: his age, the economy, and voters who won’t be won over on issues like abortion or democratic principles. In his announcement video on Tuesday, Mr. Biden devoted almost all of his attention to rights, freedom, democracy and abortion. He’ll probably need a way to speak to people who are animated by more material, economic concerns than abstract liberal values.