President Obama began his presidency vowing to negotiate an Israeli-Palestinian peace. He backed off in the face of both sides’ obstinacy and after a series of diplomatic missteps. Since then, the stalemate, and the mistrust, have only deepened, and it is clear that nothing good will happen until the United States fully engages.

The outlines of a deal are no secret. They were first proposed by President Bill Clinton in 2000. But neither side has been willing to make the necessary concessions — on land swaps, how Jerusalem can be shared and how many displaced Palestinians can go home, or not. The Israelis need to know that their closest ally won’t enable more inaction. The Palestinians need to know they will have American support so long as their demands are realistic. Mr. Obama needs to speak up before Prime Minister Benjamin Netanyahu of Israel pre-empts the debate with what is certain to be an inferior proposal when he addresses a joint meeting of Congress next month.

Mr. Netanyahu has made some concessions, most notably giving Palestinians more control over their own security in the West Bank. But he has long insisted that the Palestinians aren’t serious about negotiating a final deal, and he is now hinting that he will unilaterally offer them an interim, step-by-step arrangement that will put off statehood to some undefined future.

He also has used the upheavals in the Middle East as one more excuse not to act, rather than a reason to reinforce Israel’s security with a durable peace deal.

Mr. Netanyahu — who is coming to speak at the invitation of Representative John Boehner, the House speaker — seems to think that the Republicans’ new power means he has carte blanche in Washington. So long as Mr. Obama sits on the sidelines, he will surely continue to believe that.

The address to Congress isn’t the only deadline Mr. Obama has to worry about. The Palestinians are threatening to ask the United Nations General Assembly — which admitted the state of Israel in 1949 — to declare a Palestinian state when it meets in September. Israel and the United States dismiss this as theater. But it is certain to pass, further isolating Israel. If Washington votes against it, as it inevitably will, it would further isolate this country.

President Mahmoud Abbas of the Palestinian Authority and his aides have been building their capacity to govern in the West Bank. But Mr. Abbas isn’t helping his cause by refusing to return to the negotiating table. He suspended talks last fall after Israel refused to extend a moratorium on settlement construction. Holding to his position only gives Mr. Netanyahu an excuse not to seriously engage.

The status quo is not sustainable, as a recent surge of violence should make clear. And the options on the ground for creating a territorially coherent Palestinian state keep narrowing as Israel steps up settlement construction in the West Bank and East Jerusalem. Israel could oust the settlers — and will have to in certain areas. But the more settlers they let in, the harder it will be politically for any Israeli leader to cut a deal.

Last month, Robert Gates made the first visit to the West Bank by an American defense secretary to reinforce Washington’s commitment to a Palestinian state. But President Obama’s peace envoy, George Mitchell, who is supposed to move the process forward, hasn’t been to the region since December.

Mr. Gates was absolutely correct when he declared in Israel that despite the uncertainty caused by the upheaval in the Arab world, “there is a need and an opportunity for bold action to move toward a two-state solution.” He was talking to the Israelis and the Palestinians. We hope President Obama was listening closely, too.