Vice President Joseph Biden Jr. used rare and decidedly undiplomatic language on Tuesday to upbraid Israel after it announced plans to build 1,600 new housing units in a Jewish neighborhood of East Jerusalem. “I condemn the decision. ...,” he said in a statement.

The Obama administration is understandably furious. Mr. Biden was in Israel working to revive Israeli-Palestinian peace talks. The word came after he had spent the day vowing the United States’ “absolute, total and unvarnished commitment to Israel’s security.”

Aides say Prime Minister Benjamin Netanyahu was blindsided by the announcement from Israel’s Interior Ministry, led by the leader of right-wing Shas Party. But he didn’t disavow the plan. And it is hard to see the timing as anything but a slap in the face to Washington.

There were conflicting reports on whether the Palestinian president, Mahmoud Abbas, would go ahead with “proximity talks” — in which George Mitchell, the Middle East envoy for the United States, is supposed to shuttle between Jerusalem and the West Bank in hopes of making enough progress to revive direct negotiations on a two-state solution. Mr. Abbas should stick with the talks.

President Obama seriously miscalculated last year when he insisted that Israel impose a full stop on all new settlement building, only to have Mr. Netanyahu refuse. The goal was — and is — just. The Palestinians are legitimately fearful that the more Israel builds in the West Bank or East Jerusalem the less likely it is to ever negotiate away any disputed territory. A settlement freeze could well have jump-started serious negotiations.

But one of the basic rules of diplomacy is that American presidents never publicly insist on something they aren’t sure of getting — at least not without a backup plan. By the time Mr. Netanyahu finally acceded to a 10-month partial halt that exempted Jerusalem, the Palestinians felt so burned that the peace effort collapsed.

It must be noted that Mr. Obama and Mr. Mitchell also failed to persuade Arab leaders to agree to make any gestures to Israel in return for a settlement freeze.

The Obama administration worked hard to get Mr. Abbas to agree to renewed talks, arguing that more stalemate was not in the Palestinians’ interest. And it made some rare headway with Arab leaders, persuading them to endorse the American proposal for talks — giving Mr. Abbas needed political cover. Suggestions that Arab leaders might now renege on that support are worrisome.

Mr. Mitchell will have to keep working all sides to move this ahead. He must continue to press Israel on the settlements issue. And if Israel is to make real concessions, it will need more than gestures from the Arab states.

Mr. Biden said on Wednesday that the administration would hold both Israelis and Palestinians “accountable for any statements or actions that inflame tensions or prejudice the outcome of talks.” That would be a very important start. We also hope that if progress lags, the administration will be ready to put forward its own proposals on the central issues of borders, refugees, security and the future of Jerusalem.

Mr. Obama has another chance to move the peace process forward. This time he has to get it right.