With President Biden’s campaign in flames, the left hopes — and the right fears — that the former first lady, Michelle Obama, emerges as a replacement. But the prospect of her running, much less beating President Trump, are not the sure things that the political class imagines.

The chorus for Mrs. Obama resembles one for the rock star, Bruce Springsteen, to jump into New Jersey’s 2002 Senate race. Fans ignored that the “Born to Run” singer had no interest in serving or in attempting the tricky political alchemy that turns name recognition and celebrity goodwill into votes.

As the effort to “Draft the Boss” picked up steam, Mr. Springsteen invoked the Civil War hero, General William Tecumseh Sherman, who Republicans begged to run for the White House. “If nominated,” Mr. Springsteen said in a statement, “I will not run. If elected, I will not serve.”

For Mrs. Obama, a closer historical analogue is President Lincoln’s only surviving son, Robert. “They didn’t want me,” he said of those who urged his candidacy. “They wanted Lincoln’s son.” In Mrs. Obama’s case, Democrats want President Obama’s wife, ignoring that spouses, like sons, are distinct individuals with minds of their own.

Regardless, Mrs. Obama’s poll numbers are, like the Maltese Falcon, “the stuff dreams are made of,” at least if you’re a Democrat. An Ipsos poll released Tuesday found her ahead by eight points, 50 to 39 percent. She was the only Democrat who beat Trump to stop the party’s nightmare of his return.

Other polls find similar results, although it’s noteworthy that some find Mr. Trump leading. In any case, first ladies are always more popular than their husbands, in large part because they’re above partisanship in ways no politician can be.

Like a car when it’s driven off the dealer’s lot, Mrs. Obama loses value as a candidate the moment she hits the road to the White House. Plus, she’d have an opponent who’s not above keying fenders and slashing tires to win an advantage.

As the Democratic nominee, Mrs. Obama would have to take positions on every divisive issue facing the nation. Vice President Harris, the Constitution’s designated replacement for Mr. Biden, has the baggage of a political career, and Ipsos found her in a statistical dead heat with Trump, 42 to 43 percent.

In any case, only one vote matters and it belongs to Mrs. Obama. It may not occur to Washingtonians that anyone would pass over the presidency offered on what partisans see as a silver platter. But yesterday, Mrs. Obama told NBC News through her communications director, Crystal Carson, that she “will not be running for president.”

The novelist, Robert Louis Stevenson, first wrote about a “fire in the belly” in an 1882 essay, and it’s since become a requirement for candidates. But the prospect of hitting the trail has always left Mrs. Obama’s guts cold.

In 2021, Mrs. Obama told the BBC that she “detests” questions about running. “Politics is hard,” she said on a Netflix special last year, “and the people who get into it … you’ve got to want it. It’s got to be in your soul, because it is so important. It is not in my soul.”

On “Today” in 2018, Mrs. Obama said, “The reason why I don’t want to run for president … is that, first of all, you have to want the job,” and she doesn’t. “I’ve never had the passion for politics.” She “just happened to be married to somebody who” does “and he drug me — kicking and screaming — into this arena.”

Also in 2018, on “Jimmy Kimmel Live,” Mrs. Obama said running was “not something that I’m interested in or would ever do. Ever.” Nevertheless, the dreamers persist in dreaming, like the New Jerseyans who pine for a Senator Springsteen who’ll never be.

Expect Democrats to keep trying to drag Mrs. Obama, kicking and screaming, into solving their problem with Mr. Biden. But their pressure seems unlikely to kindle a spark in her belly or convince her to become a politician at last, one that flip-flops on years of Shermaneque denials and declares herself born to run.