Pay up, D.C.

Thirty days after winning the election, 43 days before taking the oath of office, Donald Trump engineers his transition to power from the 26th floor of the tower that bears his name on Fifth Ave. at 56th St., in the center of the nation’s most congested city. That is his home and office, and building his administration there is his prerogative as the duly elected 45th President of the United States.

But Trump’s constant presence at the site has created a security test of historic proportions — the cost of which city taxpayers must under no circumstances be left to shoulder.

Protecting the President-elect is foremost the job of the Secret Service. But there is no way a team of federal employees, however skilled, can manage the challenge that Trump presents.

The NYPD must post officers at screening checkpoints. Route pedestrian and car traffic accordingly. Route traffic disrupted by motorcades and security operations. Provide motorcade protection for all members of the Trump family as they move around, in and out of the city.

Those are only the most obvious tasks. More complex, classified security imperatives surely cost much more.

Though a police force of 35,000 officers that has managed everything from the UN General Assembly to Times Square on New Year’s Eve is surely capable of absorbing some of those tasks in stride, juggling the duties while keeping the city safe and reasonably orderly for an uninterrupted three-month stretch is another matter entirely.

The de Blasio administration crunched numbers and came up with a price tag for the entirety of the transition: $35 million.

Congress dug deep in its pockets and found, in a budget bill to be voted on Friday, $7 million. No, no, no. Never mind that New York sends billions more to the federal treasury than it gets back.

Never mind that Congress reimbursed Chicago for three fourths of the cost of protecting Barack Obama’s home during his transition — even though he was mostly working out of D.C.

Never mind that Trump chose to set up shop in Manhattan instead of the taxpayer-funded transition office that the feds make available in the capital — of which previous Presidents-in-waiting have taken advantage.

Never mind that Trump also has homes in Florida, New Jersey and elsewhere, all of which would have been less arduous to safeguard.

Never mind that Trump himself, a lifelong resident of New York, surely appreciates the strain being placed on his hometown government.

It comes down to this: Protecting the President-elect is a federal obligation.

If Speaker Paul Ryan and Senate Majority Leader Mitch McConnell see fit to stiff New York, and force its taxpayers alone to swallow a pill that should be broadly shared, they ought to get an angry call — or perhaps a tweet — from a higher authority. We hear he can be pretty demanding.