The conventional wisdom held that Mahmoud Ahmadinejad, the disheveled, Holocaust-denying, homophobic Iranian president, was the best asset of those, led by Israel, who were warning against the dangers posed by the Islamic Republic’s global ambitions.

If this man, so obviously unpleasant and quite possibly unhinged, was the elected public face of the regime in Tehran, then that regime had to be pretty terrifying. So long as president Ahmadinejad was in place, it was relatively straightforward for Israel’s Prime Minister Benjamin Netanyanu to galvanize international alarm at the prospect of a nuclear-armed Iran.

Now, though, with the succession of Hasan Rouhani to the presidency, the limits of such wisdom are becoming all too plain. In retrospect, Ahmadinejad’s eight-year spell in the job worked spectacularly well for the Islamic Republic because it creates so profound a contrast to the new, smiling, seemingly unthreatening president. Now that the Iranian leader at the UN podium is a soft-spoken cleric who’s really sorry that Jews and anybody else were killed by the Nazis, says Iran is a pussycat state that endangers absolutely no one, and speaks more than enough English to send messages of friendship to the American people in television interviews, the international community is falling over itself to welcome not just Rouhani but the apparently remade nation he now represents. After all, he is its elected president — a changed people’s changed choice of leader.

In truth, Rouhani, like Ahmadinejad before him, represents only what the regime wishes him to represent. He serves as president at the supreme leader’s discretion, one of just half a dozen candidates given permission to run in June’s election by Ayatollah Ali Khamenei. He was perceived as the most reform-minded candidate, and as such his victory does say something about the mindset of the Iranian electorate. But that mindset was never in much doubt; even before 2009’s brutally crushed mini-outburst of public protest, tens of millions of ordinary Iranians were widely understood to have become alienated by the repressive excesses of the regime.

Khamenei is likely to give Rouhani additional leeway on the international stage, while perhaps allowing a little well-controlled opposition to flare publicly at home

Khamenei’s advancement of Rouhani, however, is looking increasingly like a masterstroke. Whether the supreme leader had this all mapped out, anticipating that Rouhani would first capture the people’s vote at home, and then sally forth to such spectacular effect overseas, or whether he has been pleasantly surprised by Rouhani’s capacity to so rapidly remake the Islamic Republic’s international image without a single substantive concession on the nuclear front, the result has surely exceeded even his most optimistic visions.

As a consequence, Khamenei is likely to give Rouhani additional leeway on the international stage, while perhaps allowing a little well-controlled opposition to flare publicly at home — a few more shoes at the airport – the better to remind world leaders of the ostensible fragility of Rouhani’s position, and thus of the ostensible imperative to act quickly and cut a deal with this improbable Sheikh Moderate before he vanishes as quickly as he appeared.

In this picture released by the official website of the Iranian supreme leader's office, Supreme Leader Ayatollah Ali Khamenei, left, gives his official seal of approval to President-elect Hasan Rouhani, in an official endorsement ceremony, in Tehran, Iran, Saturday, Aug. 3, 2013. (photo credit: AP Photo/Office of the Iranian Supreme Leader)

In this picture released by the official website of the Iranian supreme leader’s office, Supreme Leader Ayatollah Ali Khamenei, left, gives his official seal of approval to President-elect Hasan Rouhani, in an official endorsement ceremony, in Tehran, Iran, Saturday, Aug. 3, 2013. (photo credit: AP Photo/Office of the Iranian Supreme Leader)

The growing concern, amid the drama that has unfolded in the less than a week since Rouhani delivered his debut address to the UN General Assembly, is that international leaders will allow themselves to be entirely seduced by Rouhani’s one-man Iran-really-loves-you show. The battle to thwart Iran’s drive to nuclear weapons is not yet lost, but it surely will be if economic pressure is lifted from the Islamic Republic irresponsibly — in the absence, that is, of verifiable arrangements to ensure that Iran does not retain the means and the material to accelerate to nuclear weapons within months.

That, after all, is what Rouhani was dispatched to the United States to set in motion: negotiations that would ease sanctions while freezing the rogue nuclear program where it is today, with Iran having mastered all the technology and mustered much of the material necessary for a rapid breakout to the bomb.

It is tempting, under Rouhani’s gentle spell, to believe that Iran truly cherishes the live-and-let-live international relationships he strives to emblemize. We all want to believe that everybody ultimately seeks to live in peace. But the unfortunate truth is that the ruthless Iranian regime that sent him to New York considers Western culture to be decadent, corrupt, and doomed — to be replaced by a global system underpinned by the ideals of the Islamic Revolution. “It is natural that our Islamic system should be viewed as an enemy and an intolerable rival by such an oppressive power as the United States, which is trying to establish a global dictatorship and further its own interests by dominating other nations and trampling on their rights,” Khamenei once told his government officials. “It is also clear that the conflict and confrontation between the two is something natural and unavoidable.” In pursuit of its goals, the regime is guilty of some of the most horrendous acts of terrorism ever committed. And it constructed key parts of its nuclear program in secret — fully intending to trick its way to a nuclear weapons capability before it was exposed.

Regime veteran Rouhani himself was part of that process, presiding over negotiations with the international community that saw the regime freeze its nuclear advance in 2003, when it believed the US would turn to Iran when Saddam was dealt with, only to secretly resume the program when the danger was deemed to have passed. To quote the proverb once memorably mangled by George W. Bush, “Fool me once, shame on you. Fool me twice, shame on me.”

It is not remotely credible to believe, as Rouhani plaintively asserts, that Iran’s nuclear intentions are entirely peaceful, and thus to capitulate in the face of Rouhani’s insistence that pressure to abandon that program is an unwarranted intrusion into Iranian national rights and must be rejected. Not when energy-rich Iran has no need for nuclear power. And not when, as the IAEA has established, its nuclear program has military characteristics.

If the Western response to Rouhani is to utilize the new possibility he brings for substantive diplomatic engagement in order to rapidly ensure the dismantling of Iran’s drive to the bomb, then his arrival to succeed the nasty Ahmadinejad will come to be rightly regarded as a blessing, however unlikely, freeing the West of the need to resort to force in order to thwart the hitherto intransigent ayatollahs.

If, however, the West melts in the warmth of a duplicitous Rouhani embrace, if the threat of military intervention is further weakened and economic pressure eased without the regime being rendered incapable of speeding to the bomb, Iran will have thoroughly outsmarted the US and those who depend on American leadership. It will have outmaneuvered a free world so wary and weary of defending itself, so willfully blinded, as to allow its most dangerous enemy the most dangerous weapon.