The US administration is exuding optimism regarding its campaign to stop the current Iranian regime from obtaining nuclear weapons. "Iran is a modern countryâ€¦ that does engage with the international community," Secretary of State Condoleezza Rice told journalists in Chicago April 19. "And so the kind of isolation that Iran is facing if it does not change its behavior is isolation that I don't think either the Iranian people or the Iranian regime can ultimately tolerate." "That is why if we are really unified and really tough in our response, I think we're going to make the diplomacy work," she said. Another senior State Department official, Nicholas Burns, said in Moscow the same day that the US had "erected a global coalition" and that "nearly every country is considering some form of sanctions; and this is a new development." Washington is now calling directly on the nations of the world not to wait for the UN Security Council, but to begin by imposing an embargo on arms sales and dual use equipment that could be employed by Iran's nuclear or missile programs. In particular, the US has asked that Russian cancel a planned $900 million sale of Tor M-1 anti-aircraft missiles to Iran. Russia's reply was hardly encouraging. "Currently, nothing is preventing the fulfillment of our obligations in the area of military and technical cooperation with Iran," Nikolai Spassky, deputy secretary of the Russian Security Council said last week. But Washington is right on all counts: Iran can be stopped, the campaign to isolate Iran is gaining steam and international unity is the key. Moreover, the shift toward encouraging nations to impose embargoes on their own, rather than putting all its diplomatic eggs in the UN Security Council basket, is an important one. Yet is far from clear that the US is acting with sufficient urgency and effectiveness. The Iranian game is simple: bob and weave for the next 33 months until the Bush administration leaves office and the threat of US military action ostensibly passes. If the UN seems ready to act, Iran can always offer to suspend enrichment again and take the wind out of the sails of the campaign for sanctions. There is no simple way to foil this Iranian strategy, though what's needed can be captured in one word: leadership. It is assumed by many that US President George Bush - floundering in the polls, reorganizing his staff, and tied up in Iraq - is unwilling or incapable of upping the ante on the diplomatic front, let alone taking military action. In reality, Bush's political problems and the Iranian threat are not in conflict, but part of the same challenge. The centerpiece of the Bush presidency is foreign policy, and that policy will have failed if the most dangerous regime in the world can run circles around the US and acquire nuclear weapons. Such a failure would certainly dwarf and possibly undo the administration's accomplishment of ridding Iraq of a similarly belligerent dictatorship. The sense that this is the direction of events, in turn, undermines Bush politically at home. It is not enough for the State Department to make vague claims about the headway it is making; significant momentum must be demonstrated. If the US, the UK, France and Germany jointly announced a tough military and diplomatic embargo on Iran as a "down payment" on future UN Security Council sanctions, these nations could make clear that Iran's game will not succeed. These are the four nations that must lead, and whose security - aside from Israel's - is most at stake. None can afford to allow Russia and China to determine the limits of the international response to Iran's current terrorist aggressions and potential nuclear threat. There is substantial agreement between Washington, London, Berlin and Paris that the mullahs must be stopped. As usual, however, it will fall on the White House to provide the leadership necessary to galvanize such a consensus into effective action. But if Bush waits too long, the sense that it is too late to stop Iran will grow, the window for action will close and his own political decline will deepen further.