On March 4, 2012, President Barack Obama told a strongly pro-Israel audience in Washington, D.C., “I have a policy to prevent Iran from obtaining a nuclear weapon. And as I have made clear time and again during the course of my presidency, I will not hesitate to use force [if] necessary ...”

Today, less than 20 months after that election-year declaration, the United States, along with representatives of the world’s other major nuclear powers, is sitting down with Iran for the second round of negotiations on ending punishing economic sanctions against Iran in exchange for Iranian pledges to forego nuclear weapons.

Iran is pushing strongly for a quick deal that would strike a “middle ground” between Western demands that it give up uranium enrichment altogether and Iran’s own insistence that it is entitled to enrich uranium. If enriched to a sufficiently high degree, uranium becomes material for making a nuclear weapon.

Iran Foreign Minister Javad Zarif told an Israeli radio program Wednesday that the talks could produce an agreement.

If Iran emerges from the talks with permission from the permanent members of the United Nations Security Council, including the United States, to continue to produce low-enriched uranium, it will inevitably retain the capability to make a nuclear weapon when it chooses.

A leading Israeli expert, Prof. Uzi Rabi of Tel Aviv University, told the Jerusalem Post that Israel must now face two facts. First, the likely agreement will allow Iran to make nuclear weapons despite the policy enunciated last year by President Obama. Second, the window for Israel to stop Iran’s forward progress toward nuclear weapons by a military strike has now closed for good.

This prospect has rightly alarmed the Israeli government and Israel’s supporters in the United States. And it calls to mind President Obama’s own assessment of the danger of allowing Iran to make progress toward nuclear weapons. In that March 4, 2012 speech the president said it would raise the prospect of nuclear weapons in terrorist hands, embolden Iran and its anti-Israel proxies, and almost certainly lead other Middle East powers to seek nuclear weapons. It still does.

In an obvious attempt to calm the fears of Israel’s supporters, former Defense Secretary and long-term Democratic Party stalwart Leon Panetta last week told the Anti-Defamation League in New York that since Iran’s Supreme Leader Ayatollah Ali Khamenei is unlikely to give up uranium enrichment, the United States “may very well have to use military force to back up our policy” against Iranian nuclear weapons.

It would be reassuring to think that a primary goal of President Obama and the other nuclear powers is to see just how far Iran is willing to go toward meeting their long-standing and essential demand that it give up uranium enrichment.

But that is not the sense delivered by the atmosphere of a major compromise in the making.

Mr. Panetta’s call for “the need to maintain a healthy skepticism” about Iran’s promises should be heard loud and clear at the White House.