That moves the calculus to Israel. It used to declare that it would never permit Iran to go past “the point of no return,” an ill-defined line beyond which Iran could rapidly produce a bomb. There’s continuing debate about where that line is, but former Israeli intelligence officials say Iran is long past it. Yet so far, Prime Minister Benjamin Netanyahu has been constrained by the United States, which argues that cyberattacks, sabotage and sanctions have been more effective at slowing Iran’s program, without creating an international furor.

The outbreak of a public debate in Israel over whether to strike soon clearly shook the Obama administration. Under pressure from American officials, Israel’s defense minister, Ehud Barak, said on Wednesday that a decision on a possible strike on Iran was “very far off.” Mr. Netanyahu’s government may calculate that if Israel is going to attempt a strike, doing so during the presidential campaign, when it would have the sympathy of many American voters, is the only way to avoid a major backlash from Mr. Obama, with whom Mr. Netanyahu has a tense relationship. Elliott Abrams, President George W. Bush’s hawkish Middle East adviser, wrote recently that if Israel attacked “Mr. Obama would be forced to back it and help Israel cope with the consequences. It might even help the president get re-elected if he ends up using force to keep the Strait of Hormuz open and Israel safe.”

IT might — or it might not. The Iranians know they have little to gain from a confrontation that spins out of control; they don’t want to take on the Fifth Fleet in the Strait of Hormuz. But threats, small attacks on refineries and harassment of shipping can send the price of oil soaring, with economic effects no leader wants in election season. Sure, Americans don’t want Iran to get the bomb. But are they willing to pay $6 a gallon to prevent it?

Instability scares the Chinese, too, but gives the Russians an opportunity. For years China resisted sanctions on Iran, since it buys so much Iranian oil. Now it sees that escalating sanctions are inevitable, so it is busy hedging its bets, looking for alternative sources (with help from the Obama administration) while delaying a crisis. “They are a little late to the game,” one of Mr. Obama’s aides said. “We have been telling them this was coming for two years now. But they are only now believing it.”

Russia is also looking to buy time, but as a significant oil producer, it benefits from a sustained crisis — as long as it stays at a low boil. The Russians have proposed a lengthy negotiating plan with Iran, one that would take years to complete. Washington sees it as a ploy that would drag out talks and give Iran time and political cover to get the bomb.

And then there are the Europeans and the Arab states. During the Bush administration they feared any tough sanctions, convinced that if they failed, President Bush would order a strike on Iran. They misread the politics in Washington; after invading Iraq, Mr. Bush was in no position to get into a conflict with another Middle Eastern country suspected of seeking nuclear weapons.

Now, exactly three years into the Obama administration, the situation has reversed. Europe is finally as eager for sanctions as Washington has been; it is preparing for an oil embargo on Iran. The United States has not purchased oil from Iran for many years, but Mr. Obama has stopped short of advocating a global total embargo, which could lead to confrontations at sea. The hard line taken by President Nicolas Sarkozy of France and Chancellor Angela Merkel of Germany has been the surprise in the latest chapter in the long-running Iranian nuclear crisis. Their operating assumption is that if the economic cost is high enough, the supreme leader will fold. Few in Washington are persuaded, but most go along with the assumption because the more forceful alternatives are too unpleasant to contemplate.

By comparison, solving the Iranian hostage crisis during the presidential election of 1980 looks almost simple. Hours after Jimmy Carter left office and the more hawkish Ronald Reagan came in, Iran freed the hostages taken at the American Embassy. When Mr. Obama or his opponent is sworn in on Jan. 20, 2013, no one expects Iran’s nuclear complex to be packed up and shipped out.