With the successful enactment of his health reform, Barack Obama has achieved his biggest domestic success so far - which, surprisingly, had greater consequences abroad than at home. The US President, whose hands had been tied in recent months by domestic concerns, and whose political power had been progressively eroded, has suddenly returned to the world stage.

Against this backdrop, the signing of a new treaty with Russia on nuclear-arms reduction, the global nuclear-disarmament initiative at the Washington conference, and an emerging new unity with Russia and China concerning further sanctions on Iran demonstrate the recovery of Mr Obama's freedom of action and operational competence.

In the process, America's new foreign-policy priorities and objectives are becoming increasingly clear. At their core lie Iran and its nuclear programme. To be sure, worldwide nuclear disarmament is in itself a central issue for the Obama Administration and, likewise, US relations with China and Russia influence many of America's other key interests. But when you look at the big picture, it becomes apparent that US foreign policy is seeking to isolate Iran internationally by means of diplomacy.

The various initiatives for nuclear disarmament are intended to build a new consensus on renunciation of nuclear weapons, which in turn would isolate and pressure Iran on its nuclear programme. Cooperation with China and Russia serves, among other things, that same purpose. And Mr Obama considers progress in the Middle East peace process essential to separating Iran from the "Arab street", thereby changing the region's balance of power for the better.

So, Mr Obama's policy towards Iran will prove to be a test of whether the US, as a world power, can defend its interests more successfully by returning to diplomacy and multilateralism, thereby dissociating itself from the belligerent unilateralism of the previous Bush Administration.

As such, the success or failure of America's policy towards Iran will become a test of multilateralism itself.

The difficulties are immense. Judging the prospects of deterring Iran from becoming a nuclear power through sanctions and diplomatic isolation requires a closer analysis of the situation in the region between the Indus Valley and the Mediterranean.

America is fighting three wars in this region: In Iraq and Afghanistan, and - not to be forgotten! - the "war on terror" against al-Qaeda and its offshoots, a war that is closely linked to the interests and conflicts within this large region. Mr Obama must finish the first two wars within his first term - or at least massively reduce US military operations - for domestic-policy and budgetary reasons, if he does not want to ruin his prospects for a second term.

Both wars are not only civil wars, but also proxy wars about regional power. The war in Afghanistan will not be decided by military force, but by the strategic interests of Pakistan and other regional powers.

Every negotiated solution with the Taliban means re-establishing Pakistan's dominance in Afghanistan, at least partially. This, however, conflicts with the goals of America's "war on terror". Besides, neither India nor Iran will simply accept such a compromise.

In Iraq, the question of power-sharing between Sunnis and Shia has neither been resolved nor secured institutionally in such a way that would definitively prevent a slide back into civil war after the majority of US troops withdraw in 2011. Another significant factor is regional rivalry between Saudi Arabia and Iran over hegemony in the Persian Gulf. The US under George W. Bush successfully destabilised Iraq and increased Iran's influence there, and the question of whether and how Iraq can maintain its stability without US military presence remains open.

As for the Middle East conflict, the conflicting interests of Benjamin Netanyahu's Administration and the American government are becoming clear. Mr Netanyahu has the choice of either losing his majority in the government and the chairmanship of his Likud party by taking up Mr Obama's peace initiative, or blocking that initiative. Everything favours his taking the second option, which will tend to lead to a standstill, and even a step back, in efforts to resolve the Israeli-Palestinian conflict.

Looking at this picture, we should not forget the global dimension, either. Today, after the world financial and economic crisis (and in contrast to 2001), the US appears to be crucially weakened. Moreover, new superpowers with their own interests - namely, China and India - have come onto the international stage.

Without the support of China and India, America's Middle East policy can no longer succeed, but this support is only granted half-heartedly - if at all.

A success for American policy in this region holds very limited interest in Beijing and New Delhi, and Europe is neither willing nor able to contribute substantial support.

In this tangled knot of regional wars, crises, and conflicts, Iran's nuclear ambitions look like a ticking time bomb - and plenty of new dynamite is being accumulated throughout the region. If the Obama Administration does not succeed in stopping Iran by peaceful means from crossing the threshold to becoming a nuclear power, a hot confrontation is lurking. It is hard to believe that Mr Netanyahu, of all Israeli prime ministers, would be the one to accept idly Iran's entry into the nuclear club.

It does not look good for Mr Obama and his Middle East policy. But if he succeeds in defusing the situation there, he would more than deserve his Nobel Peace Prize. In any case, he deserves every conceivable support.

The author, Germany's Foreign Minister and Vice Chancellor from 1998 to 2005, was a leader in the German Green Party for almost 20 years.

© Project Syndicate/Institute for Human Sciences, 2010, www.project-syndicate.org.