An old bunker at an observation point on Mount Bental in the Israel- controlled Golan Heights in 2014. (Ariel Schalit/AP)

WITH SYRIA in chaos and Iran seeking to entrench its forces there, Israel has good reason to retain control of the Golan Heights. There is, at the moment, zero international pressure on the government of Benjamin Netanyahu to consider yielding the territory, and that is likely to be true for the foreseeable future. President Trump’s tweeted announcement Thursday that the United States will recognize Israel’s annexation of the Golan might consequently be written off as gratuitous — except for the damage it will do to U.S. diplomacy, in the Middle East and beyond.

For more than half a century, one of the foundations of U.S. Mideast policy has been U.N. Security Council Resolution 242, which called on Israel to yield lands it occupied in the 1967 war for peace with its Arab neighbors. Mr. Trump’s casual ratification of Israel’s annexation, which Washington had resisted since 1981, adds an obstacle to any future peace negotiations between a reconstituted Syria and Israel. Previous Israeli governments, including under Mr. Netanyahu, considered a Golan-for-peace deal; what will be the basis for a settlement in the future?

We’re guessing Mr. Trump did not consider that question. Nor did he likely weigh the impact his decision may have on U.S. efforts to prevent other nations from absorbing territory seized by force — such as Russia’s annexation of Crimea. The U.S. action will surely encourage Israeli parties that have been agitating for the unilateral annexation of parts of the Palestinian West Bank; now that a precedent has been set, the United States can be pressured to recognize that, too.

Mr. Trump’s decision might be more defensible if it were part of a new and innovative U.S. policy in the region. But, like the move of the U.S. Embassy to Jerusalem, it appears unattached to any strategy other than rewarding Mr. Netanyahu, who has become one of Mr. Trump’s most conspicuous international supporters. The president’s tweet came as his ally struggles to fend off pending corruption charges and a stiff challenge in an election due April 9. No one will be surprised if more favors are dispensed when the Israeli leader visits the White House next week. Mr. Trump, like several presidents before him, is trying to sway an Israeli election — only unlike Barack Obama and Bill Clinton, he seeks to help rather than hurt Mr. Netanyahu.

The Israeli leader is, of course, doing his best to exploit his bond with Mr. Trump, including plastering the country with billboards showing the two of them together. Abandoning what was once a standard Israeli practice of cultivating bipartisan support in Washington, Mr. Netanyahu has bonded himself to the Republican Party and its polarizing leader. Perhaps that will help him win an unprecedented fifth term as prime minister. The likely damage to long-term Israeli-U.S. relations is a price he and Mr. Trump appear happy to accept.