On Saturday, President Trump slung a nickname at Governor DeSantis of Florida — “Ron DeSanctimonious.” Striking for its lack of stickiness and poor timing, the misfire demonstrates the challenge Mr. Trump faces if the governor seeks the White House in 2024.       

“We’re winning big in the Republican Party for the nomination like nobody’s ever seen before,” Mr. Trump told a crowd in Pennsylvania. “There it is,” he said, pointing to a poll of potential primary opponents. “Trump at 71 percent, Ron DeSanctimonious at 10 percent.”

I asked Charles Leerhsen, ghostwriter for Mr. Trump’s book “Surviving at the Top,” what he thought of the nickname. It struck me as off; the hard C between the N and T in “DeSantis,” say, fails to prickle the ear the way the Democratic slur “DeathSantis” did during the pandemic. 

“I can assure everyone that he did not come up with the Ron DeSanctimonious line,” Mr. Leerhsen said. “Yes, it is not great overall, not especially clever sonically and the timing is bad. But I feel very confident in saying that ‘sanctimonious’ is too long and too uncommon a word to be in Trump’s vocabulary.” 

Note that Mr. Trump built his businesses and campaigns on branding, often playing off confirmation bias to undermine opponents such as “Little Marco” for Senator Rubio, “low-energy Jeb” for Governor Bush — both Republicans of Florida — and “Sleepy Joe” for President Biden.

Choosing such a clunky moniker for Mr. DeSantis makes me wonder if Mr. Trump has lost his mojo, and — as Mr. Leerhsen supposes — was desperate enough for something to slow Mr. Desantis’s rising star that he took the rare step of employing someone else’s idea.

The nickname also misses the mark because it’s a play on “sanctimonious.” Coming from a twice-impeached president under a slew of investigations, it highlights those weaknesses rather than any of Mr. DeSantis’s.

At a time when many Republicans are looking for a new standard bearer, it comes across like a crime boss complaining that Commissioner Gordon is the only cop in Gotham City who refuses to take a bribe. 

Lashing out on the weekend before Election Day doesn’t work, either. This Tuesday, Mr. DeSantis is poised to do what Mr. Trump could not: Win reelection to office — and in a landslide to boot. The FiveThirtyEight polling average gives the Republican a 10.7 percentage point lead over the former governor, Democrat Charlie Crist. 

Choosing the best moment to strike is another strength that seems to have “DeSerted” the former president. Rumored as a White House candidate as far back as 1988, he waited until he benefited from being an outsider running against Secretary Clinton. 

Mrs. Clinton was so familiar in Washington, she might have been tagged with the nickname of President Theodore Roosevelt’s eldest child, Alice Roosevelt, known as “the Other Washington Monument,” and after two Democratic terms, trends favored a changing of the guard in 2016. 

The stars aligned with the help of Mr. Trump’s nickname for Ms. Clinton, “Crooked Hillary,” which kept legal and ethical questions about her character top of mind for voters, which is just where DeSanctimonious will keep Mr. Trump’s.

Another strength of Mr. DeSantis is that he refuses to be baited, the discipline you’d expect from a former Navy commander and judge advocate general. Rather than fire back at the insult, he left it to conservatives — including Mr. Trump’s secretary of state, Mike Pompeo — to mount a defense. 

By Sunday, Mr. Trump may have realized his error, telling a Miami crowd, “You’re going to elect DeSantis as your governor.” The only time he mentioned his nemesis, it was not as an endorsement, just a statement of fact. 

Nevertheless, the crowd erupted into cheers. That sound — unlike “DeSanctimonious” — is something that will become familiar to voters should the governor run for the GOP nomination, and it looks like Mr. Trump has already grown tired of hearing it.