Governor Youngkin of Virginia is suddenly being touted as a late entry into the Republican field by those desperate to dethrone President Trump. It’s a role Governor DeSantis of Florida still hopes to fill, but his fall from grace — and those of many dream candidates before him — provides a warning against believing one’s own hype.

On Saturday, Politico reported that the DeSantis campaign “is shedding staff as it navigates a cash crunch and looks to refocus resources on Iowa.” It’s a stark reversal of fortunes for a candidate who was expected to deny Mr. Trump a third Republican nomination, a feat that was only achieved once before, by President Nixon, and that even President Grant failed to perform.

Mr. DeSantis, as I wrote in May, stumbled out of the gate with a glitchy, audio-only announcement on Twitter Spaces. In the weeks since, he has been just as underwhelming, and now high-profile donors and backers, such as the head of News Corp., Rupert Murdoch, are looking to switch horses to Mr. Youngkin.

Mr. Youngkin raised GOP hopes last week when his Spirit of Virginia PAC launched “Secure Your Vote Virginia,” encouraging citizens to vote early, either in-person or absentee, saying this “is how Republicans win” and to overcome Democratic efforts to bank ballots before Election Day.

 Being a blank slate on the national stage is enabling voters to fill in the blanks about Mr. Youngkin with all their ideal qualities just as they did for Mr. DeSantis, a form of projection that has repeatedly failed to deliver once a candidate announces his run.

Dozens of Americans touted as the next president appear as footnotes in the history books. In the Spanish-American War of 1898, Admiral George Dewey was celebrated for triumphing at Manila Bay and feted with a victory arch at New York City’s Madison Square Park the following year.

Dewey’s White House prospects proved as temporary as the arch, which began to crumble soon after the hero’s victory parade. Wrote the Sun at the time: “Admiral Dewey’s announcement that he is ready to accept a nomination to the presidency is generally regarded in Washington as merely another of the absurd and lamentable mistakes that he has been led into making.”

After his heroics, the Dewey candidacy was coveted by both major parties, but twenty-three months later, the Sun reported that “nobody takes it seriously.” The billionaire mayor of New York City, Michael Bloomberg, followed the same course for Democrats in 2020, a sure-fire nominee until he began his run.

In 2016, many Republicans backed another governor of Florida, Jeb Bush, who they said had a pedigree and war chest that made him invincible. Even hyped candidates who made it like Presidents William Henry Harrison, Taylor, and Hoover fell short of the storybook endings boosters envisioned.

This curse reminds me not of a candidate hyped for the presidency but of the “M*A*S*H” star, McLean Stevenson, who was the cousin of two: Vice President Stevenson in 1896 and the Democratic governor of Illinois, Adlai E. Stevenson II, the Democratic nominee in 1952 and 1956, campaigns the actor served as a press secretary.

“M*A*S*H” was a hit and Stevenson’s character, Henry Blake, made him a superstar — or so he thought. His career spun into a crash after he left the show to headline a variety show, which flopped, and a sitcom, “Hello, Larry,” whose name lives in infamy as synonymous with failure.

“I probably got too big for my britches,” the actor said. “The biggest mistake I made was I thought everybody loved McLean Stevenson. It was Henry Blake that people loved. So, when I went out and did ‘The McLean Stevenson Show,’ nobody gave a damn.”