Israel’s concern about the specter of a nuclear Iran has now degenerated into a crisis of confidence concerning the United States. Prime Minister Binyamin Netanyahu has embarked on a campaign to force President Barack Obama to set a red line that Iran must not cross, lest it risk unleashing an American military response. Implicit threats of a unilateral Israeli attack, together with conspicuous meddling in the US presidential election campaign, have compounded Netanyahu’s effort to twist Obama’s arm.The controversy between the two allies partly reflects their divergent time lines: for Israel, the red line is Iran’s imminent burial deep underground of its uranium-enrichment facilities; for the US, it is the start of a dedicated weapons program. But, equally important, the dispute underscores their different objectives.For Israel, war with Iran is not about neutralizing an existential threat; it is about reasserting its regional status. Israel’s leaders see their country’s standing in the region being  seriously threatened by the emergence of a hostile Islamist regime in Egypt; the possibility that a similarly hostile regime will eventually emerge in Syria; the fragility of traditionally friendly Jordan; and the dangerous boost that the regional Islamist awakening has given to Israel’s sworn enemies, Hamas and Hezbollah.Both Netanyahu and Defense Minister Ehud Barak thus regard an attack on Iran as a major strategic move aimed at the broader Middle East, which implies that they would not discount a military campaign that goes well beyond surgical air strikes. Indeed, they probably contemplate land incursions into Iran, and possibly a decisive – and, from their perspective, long overdue – showdown with Hamas in Gaza and Hezbollah in Lebanon.Though determined to prevent Iran from acquiring nuclear weapons, even if doing so requires military action, the US weighs the consequences of a military showdown in very different terms. A superpower that has earned only frustration in its abortive efforts – whether war or regional diplomacy – in the dysfunctional Middle East, the US faces the Iran crisis in the midst of its epochal strategic shift to Asia and the Pacific. The fallout from a war in Iran would pin down the US in the Middle East for years to come, undermining its new strategic priorities.As a result, the US, though certainly better equipped than Israel for a war to ensure that Iran forever abandons its nuclear ambitions, could nonetheless conclude that that objective is simply too costly. The recent report by The Iran Project, whose signatories include the former US national security advisers Brent Scowcroft and Zbigniew Brzezinski, concluded that an American military attack on Iran could only delay its nuclear program for up to four years.To guarantee that Iran never acquires a nuclear bomb, the US would need to maintain military pressure on Iran for several years. And, if forced to impose regime change as the ultimate solution to the dilemma, the report assumes that this would require military occupation, which would entail a commitment of resources and personnel greater than what the US invested in the Iraq and Afghanistan wars combined.Moreover, the conventional assumption that the region’s Sunni Arab regimes would give tacit approval to a military attack on Iran’s nuclear installations must be revisited in the wake of the Arab Spring – particularly in the aftermath of the recent, sudden upsurge in anti-American violence throughout the Muslim world. The pre-Arab Spring paradigm that framed the Middle East as being divided between "moderates” and "extremists” has become obsolete.The Islamist governments that have emerged from the downfall of America’s puppet regimes are no friends of an Iranian nuclear empire. But, in their struggle to survive, they must channel popular anti-Americanism. For Egyptian President Mohamed Morsi, that imperative meant placating the angry mob that recently attacked the US embassy rather than merely condemning the violence.An attack on Iran, especially if it develops into a longer war involving regional proxies, is bound to become the trigger for mass anti-Israel and anti-US hysteria, which might draw the Islamist regimes in the region into a dynamic of escalation. It would be impossible to rule out a regional war.The main problem facing a military operation in Iran is the need to ensure its legitimacy. China and Russia would never allow the US to secure a United Nations mandate for an attack. Moreover, while Iranian provocations that clearly reveal the regime’s intentions to develop a nuclear-weapons capability might help build support for American military action, it is far from certain that Europeans, or others, would rush to join another US-led "coalition of the willing.” The dire legacy of Iraq and Afghanistan weighs heavily on the Western democracies.The saddest part of the story is Israel’s utter indifference to the need to build international legitimacy for its drive to stop Iran’s nuclear program. Netanyahu thinks in bold military terms, not in terms of geopolitical strategy. His careless Palestine policy has left Israel with few friends in the international community, let alone in the Arab Middle East. Indeed, many regard Netanyahu’s Iran obsession as nothing more than a successful ploy to divert attention from the Palestinian issue.Only a generous, bold peace initiative that would genuinely revive the two-state solution, accompanied by a freeze on construction and enlargement of West Bank settlements, would help to recover the good will of the Palestinians and their brethren throughout the Arab world. And only that outcome can secure the international goodwill that both Israel and the US will need for a showdown with Iran.Shlomo Ben-Ami, a former Israeli foreign minister and internal security minister, is Vice-President of the Toledo International Center for Peace.Copyright Project-Syndicate.org