What happens when a politician’s interest diverges from his party’s interests? That’s the question facing the Democratic Party, and it is the subject of today’s newsletter.

President Biden has survived the initial fallout from his shocking debate performance last month, and the momentum against him within the Democratic Party appears to have slowed. But the party’s basic problem is unchanged: His presence on the ballot seems likely to hurt the Democrats’ chances of beating Donald Trump this fall — and hurt the party’s chances of controlling Congress.

Among the evidence: In public appearances, Biden continues to confuse facts, and he struggles to make clear arguments for his candidacy. About 75 percent of voters say he is too old to be president, polls show. Most Democratic voters don’t want him to be the nominee, polls also show. His approval rating is below 40 percent, worse than any modern president who has gone on to win re-election.

Notably, in every battleground state that has a Senate race this year, the Democratic Senate candidate is winning, and Biden is losing:

In an earlier era, when the country’s political parties were stronger, Democratic officials might have forced Biden from the race. In 1974, senior Republicans famously persuaded Richard Nixon to resign. In 1944, when Franklin Roosevelt was ailing, Democratic power brokers ousted his Soviet-friendly vice president, Henry Wallace, from the ticket and replaced him with Harry Truman.

Today, the parties are weaker, and Democratic officials seem loath to confront Biden. (Daniel Schlozman, a political scientist at Johns Hopkins, argued in a recent Times Opinion essay that Democratic delegates do have the power to replace Biden.) For now, Democrats find themselves with a nominee whom most of them don’t want, and they don’t know what to do about it.