The New York City suburbs are not exactly the definition of a Republican stronghold, so on the eve of a rare campaign rally there, former President Donald J. Trump tried out an unorthodox pitch.

Inflation, he wrote on his social media platform, is “eating your hearts out.” Hundreds of thousands of migrants are flocking to the state while New Yorkers “are fleeing” for less expensive alternatives, he said. Put him in office, Mr. Trump added, and he would even restore the lucrative state and local tax deduction he capped as president.

“What the hell,” Mr. Trump wrote in all capital letters, “do you have to lose?”

Call it hubris or political cunning or an old-fashioned fantasy by a son of Queens, but Mr. Trump’s decision to expend one of the 49 days left in the race rallying at the Nassau Coliseum on Long Island on Wednesday has left political strategists in both parties slightly confused.

To wit: The last Republican to carry New York was Ronald Reagan. Mr. Trump’s own campaign is not meaningfully spending in the state. And despite Mr. Trump’s insistence that he has a “real chance” of winning, recent polls have shown him no closer than 14 percentage points behind Vice President Kamala Harris.

Democrats are happy to watch him while away precious days anywhere but in battlegrounds like Pennsylvania and North Carolina.

“Listen, he could spend every day in this state, and I’ll be happy,” said Jay Jacobs, the chairman of New York’s Democratic Party.