This is what blackmail looks like.

Israel will start a war with Iran and inevitably drag America into this war — unless President Obama makes a promise. He must promise that the United States will start the war at the time of Israel’s choosing.

Here’s how Amos Yadlin, a former chief of Israeli military intelligence and now director of Israel’s Institute for National Security Studies, presents the bargain, based on the premise that Israel’s window of opportunity for attacking Iran will shortly close:

On Monday, Mr. Obama and Prime Minister Benjamin Netanyahu of Israel are to meet in Washington. Of all their encounters, this could be the most critical. Asking Israel’s leaders to abide by America’s timetable, and hence allowing Israel’s window of opportunity to be closed, is to make Washington a de facto proxy for Israel’s security — a tremendous leap of faith for Israelis faced with a looming Iranian bomb. It doesn’t help when American officials warn Israel against acting without clarifying what America intends to do once its own red lines are crossed.

Mr. Obama will therefore have to shift the Israeli defense establishment’s thinking from a focus on the “zone of immunity” [the point at which Iran’s nuclear program is invulnerable to an Israeli attack] to a “zone of trust.” What is needed is an ironclad American assurance that if Israel refrains from acting in its own window of opportunity — and all other options have failed to halt Tehran’s nuclear quest — Washington will act to prevent a nuclear Iran while it is still within its power to do so.

I hope Mr. Obama will make this clear. If he does not, Israeli leaders may well choose to act while they still can.

So here we approach another war and whether the war comes sooner or later hinges on whether the Israelis have the courage to trust Obama and whether Obama is indeed worthy of such an enormous leap of faith.

In this drama the Israelis cast themselves with the nobility to exercise restraint, the daring to take on a challenge from which others might shrink, and the vision to foresee dangers about which the rest of us are less alert.

Can Obama and can the United States ascend to such moral heights? Tune into to next week’s AIPAC conference to find out.

But wait a minute. The red line that the Israelis want Obama to pledge his commitment is a red line that most observers say Iran has already crossed: acquiring nuclear weapons capability. It already has a stockpile of enriched uranium sufficient to make several weapons by most estimates.

So while Netanyahu badgers Obama to promise war, the question shouldn’t be whether at the appointed time this war kicks off; instead it should be — given that Iran has crossed the red line that Israel set — why has Israel not already launched an attack?

The truth is that is that this war that Israel insists must be fought is a war that Israel would much prefer the United States to fight and pay for on Israel’s behalf.

If Israel’s interests and those of the U.S. were truly the same when it comes to Iran, then neither should need to cajole the other into action. The current tension is instead a reflection of the fact that the two countries interests are not the same.

Indeed, the objective which at this point is still only gradually being wheeled into position is a goal utterly beyond Israel’s much vaunted military capabilities: regime change in Tehran.

And even though that goal has not explicitly been adopted by the Obama administration, Obama’s language already hints at capitulation to Israeli and rightwing pressure. His choice of metaphor for describing pressure on Iran is one which any political leadership would treat as a mortal threat.

A noose is never tightened in preparation for negotiations or compromises.