At a ceremony on Saturday, in which Khamenei endorsed Rohani, the latter pledged to do all within his power to lift the "criminal" sanctions imposed on Iran and improve its ties with the international community. But the greatest challenge facing the incoming leader is the economic crisis that has hit the country, the unemployment rates that have reached 45 percent among the country's young citizens, the 35 percent inflation and the global embargo on Iranian oil, which has blocked its ability to turn its natural resources into capital.

Rohani's success will be judged by the headway he makes in the international arena. Two fundamental questions are raised: How much time does the Iranian president need to prove that he is a moderate, rational proponent of human rights – or in other words, a liberal? And how long before he is demanded to halt Iran's nuclear program? Seemingly, these are two separate issues; an Iranian president can be a liberal while also pursuing a nuclear program, which is a cornerstone of his country's national security. Alas, the West does not see it this way. The new president's moderation, the rationality and the liberalism will be judged from now on by the familiar litmus test: Will he halt the atom program, or continue playing his predecessor's game in a more polite, cultured manner? Everything else – the release of political prisoners, the promotion of women's rights, the expansion of the freedom of expression – is inconsequential.

The United States has given Iran a yearlong extension, and suspended the discussion of the military option until June's presidential election, but this wasn't meant to allow the new president an opportunity to undo the damage caused by his predecessor, Mahmoud Ahmadinejad. The purpose of the extension is to test a diplomatic option with a new Iranian partner, while also examining the extent to which sanctions can stir political change.

The surprise election of Rohani – the only jurisprudent candidate in the bunch, a gray man who is not in the supreme leader's inner circle – indicated that rational political rules can be applied in Iran after all. But it happened at a time when Iran's economic situation is among the most difficult in history, and when the country has found itself closest to the first military attack since the Second World War. Iran's maneuvering area has shrunk and the regime's ability to survive in the face of domestic pressure depends, yet again, on capitulation to foreign demands.

Rohani is not just the great hope of the young generation, which is expecting an economic revolution. Western countries, and primarily the United States, hope for an Iranian president who won't drag them into another war in the Middle East, especially considering they have just pulled out of Iraq and are preparing to end their military involvement in Afghanistan. These nations want the incursion in Libya to be the last intervention that aims to replace a regime. In that sense the circumstances favor Rohani.

True, the ultimate decision on uranium enrichment lies with the Supreme Leader Khamenei, but Rohani is tasked with of providing Khamenei with a reason to change his policy. For that, he will need significant cooperation from the U.S. – with whom he already said he wishes to have a direct dialogue. Rohani's ambitions have not been blocked by Khamenei, despite another round of sanctions imposed by the U.S. last week.

Such a dialogue would require not only a timetable for suspending uranium enrichment, and ultimately ending enrichment altogether; the difficulty lies with questions such as who will give up what, how, and at what cost. Though Rohani's rhetoric – a skill he has already mastered in the past – will play an important role, it will not be enough. The amount of suspicion and disappointment on both sides is too big to be quelled by soft, polite language.