Tipping points in political change are based on psychological thresholds, which are both difficult to predict and measure. Often the very people who know the country best are least able to foresee the change, rooted as they are in old assumptions of stability.
Fourth, although the international community often has little to do with sudden authoritarian collapse, it can play a critical role in the immediate aftermath. No Western government has pushed Tunisia hard on democracy and human rights in the past 10 years and none can take any credit for the end of the dictatorship. The United States and other Western governments can, however, play a vital role now.
The departure of Ben Ali does not necessarily signal a democratic transition. Some authoritarian systems offer up the ouster of a president in the hopes of keeping the rest of the repressive system in place. They promise elections that will be held but then quietly shut off the oxygen to the political transition process once the international attention fades. Washington and other Western capitals should press now to get specific commitments from the new Tunisian leadership that not only will elections be held, but that they will be meaningful—that there will be genuine space and time for political parties to organize and campaign; freedom of expression, association, and movement will be respected; the elections will be administered by independent authorities; and international observers will be allowed.
Washington largely missed the boat on helping Tunisians during their dark years of dictatorship; let's not miss the chance to make up for that now with meaningful pro-democratic engagement.