PRESIDENT TRUMP on Wednesday signaled a dangerous retreat from the Middle East policy that Republican as well as Democratic presidents have pursued for the past two decades. In a news conference with Israeli Prime Minister Benjamin Netanyahu, Mr. Trump said he “can live with” a solution to the Israeli-Palestinian conflict that creates a single state for both peoples, rather than separate Israeli and Palestinian entities. He did so while strongly asserting his desire to broker “a bigger and better deal” in the region. In fact, by retreating from the two-state formula, the president has made the already slim prospects for an accord even more remote — and increased the chances that one of the few relatively peaceful corners of the region will return to conflict.

Mr. Trump cast his policy shift — which contradicted the position of not just President Barack Obama, but also Presidents George W. Bush and Bill Clinton — as a matter of acting as a neutral broker. “I’m looking at two states and one state. I can live with either one,” he said, depending on what the Israelis and Palestinians agreed to. But there is no workable one-state formula under which Israel would remain both a Jewish state and democratic. Palestinians rightly say a single state would have to grant them equal rights, including full voting rights. Most Israelis who favor it imagine an apartheid-like system in which Palestinians would live in areas with local autonomy but without either sovereignty or the same democratic rights as Jews.

Mr. Trump may have been trying to accommodate Mr. Netanyahu, who has been under tremendous pressure from his far-right coalition partners to abandon the two-state formula, which he endorsed in 2009. For his part, the Israeli prime minister declined to restate his support for Palestinian statehood, instead insisting that peace would require Palestinians to recognize Israel as a Jewish state and accept Israeli security control over all of the West Bank.

Both leaders indicated they will seek to pursue a new diplomatic avenue — first proposed last year by Mr. Netanyahu — in which Israel would develop closer ties with Arab Sunni states, which presumably would help broker a settlement with Palestinians. But Saudi Arabia, Egypt and Jordan will never support a deal in which Palestinians do not have full political rights; Mr. Netanyahu, at least, surely knows this. His proposal for a regional initiative is less a serious peace plan than a dodge. By naively embracing it, Mr. Trump has set himself up for diplomatic failure. He also has raised the odds that Palestinian frustration will spill over into a new wave of violence.

To his credit, Mr. Trump did seek to check Mr. Netanyahu in one area: settlements. The Israeli leader, who recently approved thousands of new West Bank housing units, responded that he would seek an agreement with Mr. Trump so “we don’t bump into each other.” A U.S.-Israeli deal limiting construction to existing communities close to Israel’s borders would have the practical effect of preserving the possibility of side-by-side states. If Mr. Trump really wants to broker a deal, he should start by pressing Mr. Netanyahu for such a commitment.