Next week’s White House visit by Benjamin Netanyahu, the Israeli prime minister, is already being billed as a make-or-break meeting. With good reason: the principal item on the agenda will be Iran’s nuclear programme and the prospects for war.

As numerous leaks and public comments attest, Israel appears closer than ever to taking military action against Iran. The drumbeats for war are coming from many directions – some of them eerily reminiscent of the build-up to the Iraq war.

As Iran steps up its uranium enrichment, the inspectors from the International Atomic Energy Agency, whose reports are filled with dry descriptions of nuclear centrifuges and cascades, are back at the centre of attention, just as they were in Iraq. Sanctions are being cranked up to squeeze the Iranian economy. There is also a growing feeling of impatience with diplomacy and the idea of negotiating with Tehran.

It is the sort of atmosphere in which ideas that once seemed far-off or dangerous can start to become mainstream and even gather a sense of the inevitable.

Yet if Mr Netanyahu really is coming to Washington to test support for a military assault, it is also increasingly clear what the answer is likely to be. While US president Barack Obama might still be sticking to the mantra that “all options are still on the table”, his senior national security officials have in recent weeks made it clear that they remain opposed to an attack by Israel or anyone else.

General Martin Dempsey, chairman of the joint chiefs of staff, said last week that it was “premature” to think about a military strike against Iran.

James Clapper, director of national intelligence, told the Senate that Iran had not yet made the decision to build a nuclear bomb. “I think they’re keeping themselves in a position to make that decision but there are certain things they have not yet done and have not done for some time,” he said. Admittedly, this is not as decisive a point as it used to be, given that Iran’s other activities have reduced the “break-out” time needed to build a bomb, but it is still an important distinction.

These are the public words of current officials. The opinion of many former members of the national security establishment is even more categorical. “No one I am aware of thinks that there is a positive outcome from a military strike,” Admiral William Fallon, former commander of US Central Command, which covers the Middle East, said last week.

Such doubts extend to the Israelis. Michael Hayden, former director of the Central Intelligence Agency, told a meeting last month that Israel did not have the capacity to cause serious damage to Iran’s nuclear programme. “They only have the ability to make this worse,” he said.

The difference in opinion between the US and Israel is sometimes put down to a question of timing, the idea being that Washington’s superior air power means it can afford to wait longer before deciding whether to attack. Yet for some former US military leaders, it is in some ways already too late.

According to General James Cartwright, who was until last year vice-chairman of the joint chiefs of staff, Iran’s understanding of the nuclear fuel cycle and the uranium enrichment process means it could open numerous facilities around the country. “Even if you could destroy the facilities, you would not destroy the intellectual capital,” he said. “If they have the intent, all the weapons in the world are not going to change that, because the knowledge is there and they’d just build it back.”

Of course, none of this means that Israel will not decide to launch a strike on Iran. Indeed, it is possible that the depth of the scepticism in Washington about the benefits of military action might convince Mr Netanyahu that he has no choice but to go it alone. But amid some of the loose talk about looming war, the reluctance of official Washington is still striking.

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