Slowly but surely President Trump is slaying the sacred cows of Palestinian-Israeli diplomacy.

Last week the State Department announced a $200 million cut in annual aid to the Palestinian Authority. Before that, America cut support to the United Nations Relief and Works Agency, a body created in 1949 to tend to some 750,000 Arab refugees from the war Israel’s neighbors launched to erase it off the map.

UNRWA now handles over 5 million refugee-camp residents in Syria, Lebanon, Jordan, the West Bank and Gaza. It exclusively tends to Palestinians, while another United Nations agency deals with refugees everywhere else on the globe.

Next, Washington reportedly plans to announce a cap of 500,000 refugees UNRWA can handle. Further, they’ll be counted as other refugees are counted instead of the expansive way only Palestinian “refugees” are counted, which includes multi-generational descendants.

Host countries will be asked to pitch in. (Jordan, a majority-Palestinian state, already recognizes camp residents as citizens.)

Most absurdly, Palestinian UNRWA clients living in camps where the Palestinian Authority, or in Gaza where Hamas, has full control, remain “refugees” despite Palestinian rule, hoping they’ll relocate to Tel Aviv or Haifa one day.

Since Jimmy Carter’s days, and more so since the Clinton-era Oslo Accords, Washington saw “refugees” as a “core issue” to be resolved between the parties, with America as referee.

It’s never been resolved. So just as in recognizing Jerusalem as Israel’s capital (another traditional “core issue”), Mr. Trump is changing tack. As expected, veteran peace processors are screaming bloody murder.

Not only them. Israeli security establishment types are concerned that cash cuts will harm security cooperation with the Palestinian Authority.

True, regardless of the $200 million aid cut, America will continue funding Palestinian security bodies. The other cut, to UNRWA, has little to do with security directly. Yet, funds are fungible and the Palestinian Authority’s president, Mahmoud Abbas, may well retaliate by diverting funds from security to welfare.

And so, “the ramifications of [Trump’s] abrupt steps will only empower the radicals,” warns a former Israeli army spokesman, Peter Lerner, in Haaretz.

Einat Wilf, the Israeli coauthor of “The War for Return,” a book critical of the demand for a “right” to return, disagrees. A vocal advocate of peace negotiations with the Palestinians, she nevertheless strongly calls for dismantling UNRWA.

“UNRWA encourages radicalism,” she says. “It keeps alive the dream that the pre-1948 status quo will return and that Israel as a Jewish state will be erased from the map. I’m not against aid to Palestinians, just against encouraging that dream.”

Jonathan Schanzer, a former Treasury Department antiterror official, argues that as Mr. Trump’s presentation of his “deal of the century” peace plan nears, Washington is seeking to weaken the Palestinian Authority.

After all, Mr. Abbas has rejected Mr. Trump’s plan before he saw it, sought to end America’s primacy in peacemaking, and continues to denounce America everywhere. So perhaps Mr. Trump thinks aid is simply bad business.

Yet Mr,. Schanzer guesses that once Mr. Trump’s plan is out, America may well renew financial aid, or even add to it in coordination with supportive Arab states.

Now vice president of the Foundation for Defense of Democracies, Mr. Schanzer observes that Mr. Trump is sharply veering away from traditional American peacemakers who “brought Israel and the Palestinians to the table as equals, as if the Palestinians have significant power.”

They don’t, and the traditional process is yet to yield peace.

That process took too seriously the Palestinian dream that 5 million “refugees” will one day flood the Jewish state.

“The current dynamic, and Trump’s expected offer, don’t recognize the aspirational, it recognizes reality,” Mr. Schanzer says.

Detractors say this is all shortsighted. Indeed, Mr. Trump’s new approach may lead to an uptick in violence — in the near term. But ultimately, Gordian knots are there to be cut.

In the long run, peacemaking will succeed if it addresses 21st-century facts, rather than 1948 hopes.

This column first appeared in the New York Post.