One of the first puzzles that new students of philosophy at Oxford University were posed by their tutors was to say what happens when an irresistible force meets an immovable object? The answer, of course, is that the words are wrong. The definitions make no sense. If something is irresistible, then it can move any object. If something is immoveable, then the force can be resisted. But there appears to be a growing prospect of such a contradictory experiment being carried out over the skies of the Middle East in the five dangerous months that remain of the U.S. administration of George W. Bush.

Washington is still digesting the remarks made last week by Shaul Mofaz, Israel's former top military man, former defense minister and candidate to succeed Ehud Olmert as leader of the Kadima party and prime minister.

"If Israel, the United States, or European intelligence gets proof that Iran has succeeded in developing nuclear weapons technology, then Israel will respond in a manner reflecting the existential threat posed by such a weapon," Mofaz told a forum at the Washington Institute for Near-East Policy.

With various nuances about the dwindling amounts of hope they invest in diplomacy, Israel's current Defense Minister (and former Labor Prime Minister) Ehud Barak and Foreign Minister Tzipi Livni (Mofaz's rival to succeed Olmert) all say the same thing. Even Benny Morris, the crown prince of Israel's revisionist historians, agrees.

"Israel will almost surely attack Iran's nuclear sites in the next four to seven months," Morris wrote in the New York Times last month. "And the leaders in Washington and even Tehran should hope that the attack will be successful enough to cause at least a significant delay in the Iranian production schedule, if not complete destruction, of that country's nuclear program. Because if the attack fails, the Middle East will almost certainly face a nuclear war – either through a subsequent preemptive Israeli nuclear strike or a nuclear exchange shortly after Iran gets the bomb."

And yet U.S. Defense Secretary Robert Gates and the chairman of the joint chiefs of staff Admiral Mike Mullen have both publicly warned against such a strike.

The crucial question emerges from the geography. It will be a stretch for Israeli warplanes to reach the putative targets in Iran. And they will almost certainly have to fly through U.S.-controlled airspace over Iraq to do so, and may even have to rescue pilots from damaged planes who parachute down into Iraq.

Given the risks and likely consequences of an Israel strike, would the United States warn Israel to abort the mission? If the Israelis called the American bluff and went ahead, would Gates and Mullen order U.S. warplanes to shoot them down, knowing that failure to do so would make the United States in the eyes of the world an accessory of the attack?

An irresistible force seems to be building in Israel. The question is whether the United States is prepared to be the immovable object.