If Michael Bloomberg really wants Hillary Clinton to beat Donald Trump in November, the former mayor of New York might want to rethink his plan to endorse her in a prime-time speech at the Democratic National Convention. Mrs. Clinton’s chances of winning would be better if Mr. Bloomberg kept his mouth shut and stayed at one of his many homes rather than traveling to the convention in Philadelphia.

What are Mr. Bloomberg and Mrs. Clinton thinking? Is there a single undecided voter out there who is really waiting for word that yet another Ivy League-educated Manhattan Jewish billionaire press magnate who made a fortune from Wall Street is against Trump? The notion that Mr. Bloomberg will sway any votes is so remotely out of touch with the reality of the 2016 electorate as to be comical.

This is the Bloomberg whose charity publicly cheers when coal plants close, putting miners out of work. The Bloomberg who opposed confirming Chief Justice John Roberts to the Supreme Court on the grounds that he was insufficiently outspoken in defense of abortion rights. The Bloomberg who himself nearly mounted an independent presidential campaign against Mrs. Clinton on the basis that her record of accomplishments was negligible and her abandonment of free trade was inexcusable.

The only suspense about the Bloomberg endorsement of Mrs. Clinton involves which of his fleet of aircraft he will use to travel to Philadelphia to deliver it. Will he ride on his helicopter? Or his Dassault Falcon 900 jet?

Who, exactly, does the Clinton campaign think Mr. Bloomberg is going to reassure? Are Bernie Sanders voters going to be pleased by a prime-time speech by a billionaire who favors the Keystone XL oil pipeline and who, as mayor, presided over a police department whose stop-and-frisk tactics were the target of a lawsuit and minority complaints?

Are the teachers unions who make up so much of the Democratic Party’s activist core going to be happy to hear from Mr. Bloomberg, who was a big advocate of charter schools? Does the Clinton campaign really think it requires buttressing in Mr. Bloomberg’s home states of New York or Massachusetts? The last time a Republican carried the electoral votes of either the Empire State or the Bay State was Reagan’s re-election in 1984.

A New York Times dispatch reporting on Mr. Bloomberg’s endorsement plans quotes a former mayor of Philadelphia, Michael Nutter, saying that Mr. Bloomberg “could help persuade other business leaders to back Mrs. Clinton, ‘in some cases Republican business people.’”

If Mr. Bloomberg’s intended audience is “Republican business people,” let him go on a speaking tour of chambers of commerce in South Carolina or Wyoming. The thing about Democratic National Conventions is that they don’t, as a rule, tend to attract many Republican business people.

I say all this as an admirer of Mr. Bloomberg who might well have voted for him if he had run for president as an independent. I like Bloomberg the Eagle Scout and Bloomberg the entrepreneur. But with the Clinton endorsement, the Bloombergs on display are the elitist and the ego.

Perhaps the Clinton campaign will attempt to portray the backing from Bloomberg, an independent, as a sign that Mrs. Clinton is somehow a uniter, unlike the divisive Mr. Trump. But any uniting being accomplished here is less a tribute to Mrs. Clinton than a consequence of Mr. Trump, the prospect of whose victory seems to have united the Upper East Side of Manhattan into something that closely resembles a panic. For more than a few Trump voters, the fact that Mr. Trump sends Mr. Bloomberg into such a tizzy may itself be reason enough to check the Republican box on the ballot come Election Day.

Ira Stoll is editor of FutureOfCapitalism.com