He has for decades regarded himself as an unrivaled titan in his hometown, gorging at the only-in-New-York intersection of real estate, media and celebrity-for-its-own-sake. His name has appeared on the facades of New York’s buildings, at the top of its V.I.P. lists and in the gossip pages whose stewards he had on speed dial.

There was no anonymous “source close to Trump,” reporters across town came to know, quite so availing as The Donald himself.

Yet in recent months, to the dismay of a great many New Yorkers, Mr. Trump has become something of an avatar for the city — the brash ambassador who defended its honor when Senator Ted Cruz of Texas used “New York values” as a slur. (Mr. Cruz was criticizing Mr. Trump’s past support for abortion rights, among other shifts.)

John Catsimatidis, a grocery store and oil magnate who is friendly with Mr. Trump and Mrs. Clinton, likened Mr. Trump to a conquering hero returning home.

“He’s coming back as the king of the world,” Mr. Catsimatidis said. “I don’t think me or you has ever seen something like this.”

When, after all, has anyone seen a New Yorker go up against a New Yorker for the right to go up against, very possibly, a New Yorker?