Could a Prominent Democrat Really Challenge Biden? It’s Unlikely.

Forty-four years ago tomorrow, the last serious primary opponent to a sitting Democratic president announced his campaign before 5,000 supporters in Boston.

But that challenge by Senator Edward M. Kennedy, who ran against President Jimmy Carter for the 1980 nomination, offers little precedent for the legion of Democrats fretting about President Biden’s standing ahead of a likely 2024 rematch with former President Donald J. Trump.

On panicked text threads and during late-night bar sessions, Democrats in the political world have thrown out the names of ambitious rising stars in the party as possible primary challengers: Gretchen Whitmer. Gavin Newsom. J.B. Pritzker. Raphael Warnock.

But it’s highly unlikely, given how much time, planning and money a presidential campaign requires, that any of them would run against Mr. Biden at this point. Challenging an incumbent president is widely seen as a career killer in politics, and virtually all of the Democrats talked about as possible Biden alternatives have thrown their support behind him.

Modern Democratic politics have also de-emphasized the traditional early states of Iowa and New Hampshire, where Senator Kennedy traveled after announcing his campaign, in favor of a diverse group of states where Mr. Biden was strong in the 2020 primary season. Mr. Biden, and before him Hillary Clinton and Barack Obama, won the nomination largely because of their strength with Black voters in Democratic primaries.

There’s also the matter of qualifying for primary ballots. Deadlines have already passed in Nevada and New Hampshire. Others are approaching on Friday in Alabama, Michigan and South Carolina. Deadlines in delegate-rich California and Florida will come by the end of the month.

A theoretical primary challenger would also have to raise tens of millions of dollars to compete with the $90.5 million Mr. Biden’s campaign committees and the allied Democratic National Committee reported having at the end of September. The party’s major donors are effectively in lock step behind Mr. Biden; a primary challenger would need to either peel off a significant proportion of them in short order or be rich enough to finance a large portion of any campaign.

Mr. Pritzker, the governor of Illinois, is helping to plan and fund next year’s Democratic National Convention. Mr. Newsom, the governor of California, has offered himself up to debate second-tier Republican candidates on Mr. Biden’s behalf. Figures like Ms. Whitmer, the governor of Michigan, and Raphael Warnock, the senator from Georgia, have shown little indication they’re at cross purposes with the White House.

And yet Mr. Biden will turn 81 this month. If anything is durable about his polling numbers, it is how weak his standing is among the party’s core constituencies. But as the old saying goes in politics, you can’t beat something with nothing.