It’s Biden vs. Trump.

To me, that’s the only real takeaway from Super Tuesday, when President Biden and Donald J. Trump won nearly all of the delegates at stake. It will still be a week or two before they officially clinch their nominations, but at this point the primaries are effectively over. The general election is about to begin.

On paper, Mr. Biden ought to be the favorite. He’s an incumbent president running for re-election against the backdrop of a healthy enough economy, and against an opponent accused of multiple federal crimes.

Yet according to the polls, Mr. Trump begins the general election campaign in the lead.

Mr. Trump’s lead is modest but clear. Over the last four months, he has led nearly every poll in Michigan, Nevada, Arizona and Georgia, along with the states he carried in 2020 — enough to give him 283 electoral votes and the presidency. He also leads in most national polls over the last month, including a New York Times/Siena College poll last weekend.

This is not what many expected from a Biden-Trump rematch, especially after Democrats were resilient in the midterms and excelled in special elections by campaigning on issues like democracy and abortion.

But Mr. Trump is winning anyway, and there’s a simple reason: Mr. Biden is very unpopular. His job approval rating is stuck in the upper 30s, and voters simply don’t look upon him favorably the way they once did. Nearly three-quarters of voters, including a majority of Democrats, say he is too old to be an effective president.

In the end, Mr. Biden might well prevail by capitalizing on issues like abortion and democracy. Historically, early polls are not especially predictive of the final outcome. Many voters aren’t yet paying close attention, and there will be every opportunity for the Biden campaign to refocus the electorate on more favorable issues once the general election campaign gets underway. The events of the next eight months will surely matter, too — from the effects of a gradually improving economy to the circumstances on the border and conflicts abroad.