America’s support for Israel has always had two justifications. One was emotional – this plucky little nation of survivors, the Middle East’s only real democracy, surrounded by wolves. The other was strategic, and, given the degree to which the region has changed over the past 40 years, its endurance is remarkable. Now though, thanks to months of feverish diplomacy and Iran’s sweet-talking new President, it looks more fragile than ever before.

In the Cold War, Israel was regarded as a powerful military ally in a region where radical Arab regimes were firmly aligned with the Soviet Union. The Iranian revolution, the first Gulf War and the rise of Islamism, all gave new life to the US Jewish lobby’s characterisation of Israel as America’s single stalwart friend in the region.

But today’s Middle East is once again on the move. Less than two months ago, a US war with Iran was still on the cards; today an historic rapprochement between those countries is not inconceivable. And while America’s sentimental support for Israel will not go away, the Jewish state risks becoming a strategic irrelevance.

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Benjamin Netanyahu is in a difficult position, particularly now that the Holocaust-denying Mahmoud Ahmadinejad has been replaced by the apparently eminently reasonable Hassan Rouhani in Tehran. Had the Israeli premier the stature of the late Yitzhak Rabin, he might use his speech at the UN General Assembly on Tuesday to signal Israel’s readiness to come clean about its nuclear arsenal and sign the non-proliferation treaty, as the Iranian President has suggested. He might also take concrete steps to bring a two-state solution with Palestine closer.

Unfortunately, Mr Netanyahu is no Rabin, and he is hounded at home by those even more hawkish than himself. Instead, he will in all likelihood stick to the script that Mr Rouhani is a wolf in sheep’s clothing and Tehran is as dangerous as ever. In doing so, he helps neither himself nor Washington nor the rest of us.