The cold wasn’t the only thing that hammered the Northeast in the final fortnight of 2017 — and we can thank our extreme political polarization for the traumas we New Yorkers and New Jerseyans are about to suffer.

On the last night of the year, the Trump administration informed New York and New Jersey that there was no longer a deal with the federal government to help fund the desperately needed new rail tunnel between the two states — a $13 billion hit.

Before that came the signing of the tax bill, whose limitations on the mortgage-interest and state- and local-tax deductions (SALT) are going to hammer upper-middle-class residents in these states and send real-estate values into a downward spiral.

We can argue about the merits of these decisions. Does the unquestionable NY-NJ commuter crisis have a national component obliging the federal government to take an active role? There are strong arguments on both sides.

Should states with high taxes have been allowed to keep their taxes high and spend so much on services not provided to other states by gaming the system through the state- and local-tax deduction?

And was there a public interest in allowing people who can afford million-dollar mortgage payments to deduct the entirety of the interest on those mortgages — or does the existence of that deduction simply inflate housing prices at every level and make home ownership unaffordable?

There are arguments on both sides here. They cannot be easily resolved.

But what we do know is this: Had there been a single Republican senator in any of the high-tax states in America — a senator in New York or New Jersey or Illinois or California or Oregon or Minnesota or Hawaii — the elimination of the SALT deduction would likely not have been included in the final tax-reform bill.

The loss of a single Republican vote in the Senate would have had potentially catastrophic consequences for final passage of the bill. This would have been known to the House and Senate, and the entire structure of the package would have been reconceived from the get-go to avoid the possibility of losing that vote.

Similarly with the elimination of the federal funding for the Gateway rail-tunnel project: A loud Republican voice in Washington advocating for the necessity of the tunnel might have had real influence on the administration.

Instead, you have Chuck Schumer and Kirsten Gillibrand hurling mud at the White House every chance they get, while New Jersey’s Cory Booker circulates an impeachment petition. (Booker’s colleague Robert Menendez has been out of the picture pretty much, owing to his legal troubles.)

What conceivable incentive does the Trump administration have politically to throw us a bone here?

America’s remarkable sorting into ideological blocs defined in part by their common geography has been the great political story of the past two decades. Now the bill is coming due.

The George W. Bush administration might have pursued the Trump model of screwing NY/NJ had it not been for 9/11 and the need for rebuilding dollars from the federal government. Then came Barack Obama, who was our friend and went the other way — pursuing energy policies that did to red states what Trump is now doing to blue states.

Is this fair? Is it right? This is how it works. This is the real world. And now we have to deal with it.

Gov. Cuomo and whoever the new guy in Trenton is are going to have to figure out how to pay for that tunnel without federal largesse — and without sticking it even more severely to the NY/NJ taxpayer since they can no longer rely on the federal tax writeoff.

Enjoy the cold, fellas. You’re going to be suffering with it for a long, long time.

jpodhoretz@gmail.com