At the United Nations headquarters in New York, President Trump is engaged in a standoff with a deeply entrenched political class.

Yet, it is the president who has the initiative.

In aggressively challenging the U.N.'s condemnation of his decision to move the U.S. Embassy in Israel to Jerusalem, Trump has the massive leverage created by the $10 billion Washington gives to the U.N. each year.

He who pays the piper calls the tune. That's the big picture. But you get still more from the details, so let's dig in.

As the Council on Foreign Relations reports, the U.S. is responsible for nearly 40 percent of the U.N.'s refugee agency, 35 percent of the World Food Programme's total budget, and more than 30 percent of the International Organization for Migration. It provides over $2 billion a year to the U.N.'s peacekeeping budget excluding the massive cost of American military security guarantees, and 22 percent of the U.N.'s operating budget.

For the sake of comparison, if an external actor were responsible for 22 percent of the federal budget, it would have to send $888 billion to the U.S. Treasury every year.

We recognize that many frontline U.N. programs do important work in saving and improving lives. But Trump is right to expect a measure of gratitude for this nation's commitments. Instead, he is receiving scorn and rebuke for practicing the most basic right of sovereign power to decide, in concert with a host nation, where to locate an embassy. The casual view at East 42nd Street seems to be: "American taxpayers, write us a check, then shut up and listen while we educate them about their nation's inadequacies."

Sorry, folks, that's not how it works. While the U.N., and many of the bankrupt cutthroats who make up its membership, have long nurtured an unveiled contempt for America and conservatives, it is they, not we, who are going to have to shape up. Trump should push unflinchingly for reform at the U.N.

First, he should double down on previously announced budgetary plans and cut U.S. spending on the U.N. by 25 percent. That figure would cause consternation in the U.N. accounting and political offices, but it would not harm lives. If the denizens of Turtle Bay are convinced of the need to act in multilateral companionship, European members could pull together the $2.5 billion or so necessary to offset U.S. cuts.

Taxpayers of those nations might not like this, but that's the point. It might prove salutary for the politicians who vote to condemn perfectly reasonable American diplomatic moves. As months go by and U.N. officials recognize that their criticisms harden Trump's resolve, he'd be well-placed to demand reforms in return for a resumed flow of greenbacks.

Trump should start with political reform. Dictatorships should get perches on U.N. councils. It is ludicrous, for example, that Cuba and Nicolás Maduro's Venezuelan "rabbit republic" sit on the human rights council. It is an insult to their oppressed people and an embarrassment to the notion of moral justice. We do not believe today's United Nations is what President Harry S. Truman had in mind when, in 1945, he called on the new organization to "build a new world — a far better world — one in which the eternal dignity of man is respected."

Next, Trump should demand an external audit of U.N. staffing, programs, and priorities.

This is necessary because, as the Guardian explains, "Even accounting for inflation, annual U.N. expenditure is 40 times higher than it was in the early 1950s. The organization now encompasses 17 specialized agencies, 14 funds, and a secretariat with 17 departments employing 41,000 people." The Guardian also reports that the "mouthwatering daily allowances which result in many of its bureaucrats being far better paid than American civil servants has more than doubled over the past two decades to $5.4 billion."

That so many billions are diverted from frontline priorities to Manhattan high-living is repulsive, and it must end.

Trump's opportunity here is that taxpayer interests, global needs, and the U.N.'s incompetence all give him both the cause and the means of moral action. It says much about an organization that the relocation of an American embassy sparks more anger than Bashar Assad's slaughter of hundreds of thousands of civilians.

Now, it's America's time to be angry and to demand change.