KYLE SMITH: There’s one thing dividing New Yorkers: Bill de Blasio.

Here’s the Bill de Blasio arithmetic for New York City: 2-1+1=2. The story of New York is “A Tale of Two Cities,” he said in his 2013 mayoral campaign.

No, make that one, he said in his many “One City” speeches in which he promised to unite us. Scratch that, he says now that he’s preparing next year’s re-election campaign: It’s still two cities.

In other words, de Blasio’s grand re-election campaign theme is: It’s Us Against Them. Call in some pitchforks and fire up the torches. The mob forms to the left. The reason for the new strategy is obvious, but I’ll come back to that.

An innuendo-laden piece of nudge-nudge appeared in The New York Times this week under the headline, “De Blasio Shifts Away from His Re-Election Message of ‘One City.’ ” The “One City” motif has been used on banners hoisted behind de Blasio at public events, in policy platforms and frequently in the mayor’s speeches.

Saying something doesn’t make it true, however. The Times reporter wrote, “The notion that Mr. de Blasio has brought about a unified city . . . appears to have all but vanished as an argument for his re-election in 2017.”

Pursued by such a broad range of investigators that things are starting to look like a reenactment of the climactic chase scene in “The Blues Brothers,” the mayor is said to feel “sapped” of the “ability to court new voters . . . especially skeptical whites who have mostly shunned the mayor’s agenda.”

He’s a debacle.