Diners — particularly the ones on Long Island — are platforms for true, unvarnished democratic debate. When I was in Congress, I didn’t need a poll. Just a deluxe hamburger platter, a strong stomach and thick skin.

I learned on Wednesday why President Donald Trump’s appalling behavior over the past week may be his winning political strategy over the long run.

I had breakfast with one of my former congressional staffers at a diner in Hicksville. Two older men took a table next to us. On the TV overhead were news images of neo-Nazis marching in Charlottesville, Virginia.

My ears perked when I heard one of the men say: “These Democrats will do whatever they have to stop the president.”

His friend agreed: “Now they’re making a big deal about statues? Who cares about statues!”

That single exchange, in hardened Lawn-Guyland accents, was more instructive than all the polished analysis and punditry I’ve read and heard.

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Here’s why:

Trump has been diabolically brilliant in deflecting attention from the one thing that can sink his re-election campaign and congressional Republicans in the midterm elections: He hasn’t gotten anything done for the middle class.

In fact, other than the failed repeal of Obamacare and the confirmation of a Supreme Court justice, he hasn’t even proposed anything to Congress. No tax reform, no infrastructure. The “great wall” he promised on “Day 1” hasn’t been funded. On foreign policy, his promise to undo the nuclear deal with Iran, — which he called “the worst deal ever” — was just certified by his own signature. He has Republican majorities in the House and Senate and little of substance to show for it.

And he has successfully avoided any sustained conversation about that Achilles heel in his presidency. We’re distracted by sharp and shiny objects like tweets and news conferences rather than the dull reality of a Republican president and Congress that haven’t produced. Democrats get pulled into a hyperbolic maelstrom — feeding the misperceptions that they are the ones responsible for inaction in Washington.

Don’t get me wrong. I believe what he said about neo-Nazis — and continues to say — is repugnant and maddening.

There’s another dynamic at work here. Republican congressional candidates know that failure to pass meaningful solutions to people’s anxieties can doom their majority next year. And that may be precisely what the Trump administration wants. After a while, the emperor will have no clothes.

Trump’s penchant for blaming everyone but himself for his missteps will wear thin. Unless, of course, Republicans lose the House majority in November 2018. What better villain for thwarting his agenda than a House Democratic majority as he seeks re-election in 2020?

It may not be the “Art of the Deal” so much as it’s Machiavelli’s “The Prince.”

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And, after listening to two Long Islanders in a diner in Hicksville, I wonder whether it just may work.

Steve Israel is a former Democratic congressman from Huntington.