In the wake of the Iranian government crackdown today it’s tempting to compare the fate of the protest movement to that held in the Spring of 1989 in Beijing. Of course, we don’t know the ultimate fate of the current protests in Iran so even superficial comparisons are premature at this point.

But there is another more profound difference between the two situations that we should keep in mind. The 1989 demonstrations that began in mid-April following the death of dissident Hu Yaobang represented a hodgepodge of activists angry at the government for a variety of reasons. While there had been momentous protests at Tiananmen Square before – notably in 1976 with the end of the Gang of Four – there was no period of democracy to which the protests could invoke. The famous Goddess of Democracy statue constructed by art students that Spring symbolized the larger aims of the protesters. But there was no tradition of electoral democracy that the protesters could claim had been illegally denied.

In Iran, of course, the cause of the current movement is the fraudulent (by most accounts) election of President Mahmoud Ahmadinejad in a country whose citizens had every reason to believe that the election would be conducted fairly (even if the candidate selection process was controlled by the clerics). Put simply: the difference between Iran and China was one of expectations. In China, the protesters expressed hopes and dreams of change, based partly on ongoing reforms facing Poland and Hungary (the other revolutions would happen in the Fall). But outside a few dissidents like Zhao Ziyang the government never committed itself to even the fiction of democracy.

This is a crucial difference because these dashed expectations in Iran undermine the legitimacy of the hybrid theocratic-democratic system of the Islamic Republic that even Ali Khamanei praises to this day. The people of Iran will never again believe that the Islamic Republic represents the democratic spirit (such as it was) of the 1979 anti-Shah movement; we often forget in the West how widely despised the Shah was, and how many liberals and feminists supported his overthrow. Though this democratic heritage, which dates to the 1906 constitution, was circumscribed by the Supreme Leader system, it was still highly valued among the Iranian population. Denial of even this limited democracy delegitimizes the entire Islamic Republic.

In China, the Communist Party’s legitimacy was never predicated upon free and fair elections. As such, the June 4 crackdown did not de-legitimize the Chinese regime the way the current violence does in Iran. The 1989 massacres obviously infuriated supporters of democracy around the world. But it never undercut the authority of a regime long predicated upon totalitarian force.

Keep this point in mind over the current days as commentators – and the Iranian government – suggest that the genie can be put back in the bottle as was done in China 20 years ago. It cannot. The Islamic Republic’s leaders who desperately crave legitimacy internally and externally will never be able to command the respect of the citizens again. The regime may limp forward as before, but it will face more and more internal unrest and external isolation. Its standing in the Islamic world will have taken a huge hit. And its negotiating position vis-a-vis the West over nuclear weapons and terrorism will be severely weakened.

Make no mistake, the Islamic Republic has suffered a devastating blow this last week. The only question now is WHEN, not IF, it will finally collapse.