Barack Obama coupled a pledge – that he was prepared to use military action if necessary to prevent Iran from acquiring nuclear weapons – with a clear warning that "too much loose talk of war" had actually been helpful to Tehran.
On the eve of a crucial meeting today with the Israeli Prime Minister, Benjamin Netanyahu, the US President repeatedly emphasised his preference for a diplomatic solution, backed by sanctions. "For the sake of Israel's security, America's security and the peace and security of the world, now is not the time for bluster. Now is the time to let our increased pressure sink in and to sustain the broad international coalition that we have built," he said, in a speech to a conference organised by the American Israel Public Affairs Committee (Aipac) in Washington DC.
In doing so, and while forcefully warning that a nuclear-armed Iran ran "completely counter to both Israel's and the US's security interests", Mr Obama did little to gloss over the issues at the heart of a disagreement between the US and Israel over their strategy towards Tehran's nuclear programme.
Key to these differences are two closely-linked issues of timing. For Israel, the "red line" comes when Iran is capable of building a nuclear weapon. According to most Israeli readings, Iran is not far off that point.
For the US administration, the red line comes significantly later, namely if and when Iran starts building, or at least decides to build, a nuclear weapon. This is why Obama chose his words carefully when he spoke of his determination to prevent Iran from "acquiring a nuclear weapon", and this why he believes there is time for sanctions and diplomatic pressure. He will tell Mr Netanyahu that these offer a more "permanent" means of solving the problem than a bombing strike that would only set back a military nuclear programme for a few years at most and might actually strengthen the Iranians' resolve.
But what if the sanctions do not deter Iran, as Israel says it fears they may not? This is the second timing issue. According to the Israeli Defence Minister, Ehud Barak, Iran may soon enter a "zone of immunity", or the point at which its nuclear facilities, including its underground enrichment plant, are beyond the reach of external attack, enabling Iran to complete a nuclear programme, safe from Israel's "bunker-buster" bombs.
By all accounts, what Israel has been saying to Washington is this: "OK, if we accept your longer timetable and we wait to see if the sanctions work, our window of opportunity for an effective military strike will almost certainly be passed. To allow that, we need in return an iron-clad commitment that the US will conduct such strikes if the sanctions fail to stop Iran building nuclear weapons. Otherwise, we may well have to go ahead on our own."
It is far from clear that Mr Netanyahu will be satisfied by Mr Obama's promise yesterday that he "will not hesitate to use force when it is necessary to defend the US and its interests".
Certainly, his warning against "loose talk of war" may be seen as a rebuke to some Israelis as well as US Republican politicians.
T he President knows Mr Netanyahu is a fairly risk-averse politician; that his ratings are strong enough not to need the severe electoral gamble of a war; that large sections of the Israeli military and intelligence establishment are opposed to a unilateral strike; and that the polls hardly indicate a popular clamour for war in Israel.
And this is despite the relatively muted public debate within the country on the potential risks of starting one, from regional conflagration to a possible increase in the support for the Tehran regime by a currently restive Iranian population.
But in a presidential election year, Mr Netanyahu also has leverage. That these talks are being held on the margins of the Aipac conference is a reminder of the influence of that body (far more representative of Israel's government than it is of most American Jews) on US politics.
But for all of Mr Obama's justifiable professions of how much he has done to foster America's relationship with Israel, his speech strongly suggests that Mr Netanyahu won't find the US President a pushover when he meets him today.
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