President Trump touted the 2020 Abraham Accords that established formal ties between Israel and four Arab countries as one of the biggest foreign policy achievements of his first term.

Now he is pursuing his long-desired goal of getting Saudi Arabia to join the accords — but he may have just dealt himself a serious setback. Mr. Trump’s proposal to transfer all two million Palestinians out of the Gaza Strip and then rebuild the enclave as the “Riviera of the Middle East” has antagonized some of the very people he needs to seal the deal.

The Gaza idea was swiftly rejected by Arab countries, among them Saudi Arabia. The Gulf powerhouse released a pre-dawn statement right after Mr. Trump floated the proposal on Tuesday evening alongside Prime Minister Benjamin Netanyahu of Israel in Washington.

The kingdom made clear that it is standing by its demand that a Palestinian state first be established before it will normalize relations with Israel. The precondition, which the Saudis have insisted on for the past year, is “nonnegotiable and not subject to compromises,” the Foreign Ministry said in a statement on Wednesday.

The statement directly contradicted Mr. Trump, who had just told reporters in Washington that Saudi Arabia had dropped the precondition. One senior Saudi royal said what the American leader was proposing would be tantamount to an “ethnic cleansing” of Gaza.