Iran is not on the agenda. But it is on their minds.

As the big United Nations meeting gets underway, the West's biggest foreign policy challenge is not likely to be discussed.

But Israel's Prime Minister Benjamin Netanyahu has bluntly demanded to know when the time will be right to use force against Iran's nuclear weapons programme.

He's asked the question so well that it has been turned into a US presidential election TV ad. The advert ends with the words: "The world needs American strength. Not apologies."

Given that Mitt Romney, author of No Apology, has repeatedly accused the president of apologising for America, it is not too hard to work out whom the ad is backing.

Of course Mr Netanyahu bears no responsibility for how others use his speeches. But Israeli officials do seem to be behind a claim that he had been snubbed by Mr Obama, who won't be meeting the prime minister at the UN.

Some in Israel say Mr Netanyahu is putting a vital relationship at risk.

He's sent a message to the White House stressing that he is not interfering in the American election on behalf of Mitt, with whom he worked in the 1970s.

So, many in Washington are asking the question: "What is Bibi up to?"

While Downing Street and the White House are united in their public and private insistence that Iran must not get the bomb, they are also deeply unenthusiastic about getting involved in another war.

Some think Mr Netanyahu wants assurances that if Israel doesn't act before the US election, there will be American action after it.

Mr Obama is not willing to give such assurances, in public or private. There is a determination, not least because of public opinion, to negotiate with Iran until it either yields results or it becomes crystal clear to everyone that further negotiations are pointless.

One well-connected insider has told me that many in the American Jewish community think Mr Netanyahu has been brazen and insolent, that his tactic has backfired.

There's a belief that superficially, what Mr Netanyahu wants is simple. He would like to pressure Mr Obama to promise he will take military action, so Israel need not go it alone. But he will not be given this assurance.

So, my insider believes that having raised the possibility of war, "made everyone's flesh creep, and marched us up to the top of the mountain", the Israel leader is now looking for a "gilded ladder" to climb down.

That may reassure the White House ahead of an election, but it still leaves open how Mr Obama or a President Romney would resolve the larger crisis.