Editor's note: Kenneth M. Pollack is a senior fellow in foreign policy studies and the director of the Saban Center for Middle East Policy at the Brookings Institution. He is the author of numerous books on the Middle East, including A Path Out of the Desert: A Grand Strategy for America in the Middle East (Random House, 2008).
(CNN) -- Egyptians deserve their time to celebrate. Hosni Mubarak's resignation is a dramatic victory for the protest movement born so suddenly on January 25. As recently as a few weeks ago, few Egyptians -- if any --could conceive of such a thing. As Americans, we should only bask in their reflected joy and allow them this moment to revel in what they have accomplished.
But the celebration cannot go on for too long because there is still much to be done if they are to realize their dreams of a prosperous, modern, democratic Egypt.
Mubarak's exit cannot be seen as the ultimate triumph of Egypt's pro-democracy protest movement, although it is an important victory on the way. Egypt's problems began before Mubarak, and they will not end with his ouster. Instead, they are the product of a corrupt, stagnant and oppressive system which Mubarak helped to build but now extends beyond his own person.
And large elements of that system remain in place. The Egyptian military, particularly its senior officers and intelligence leadership, have been critical pillars of that system, and neither we nor the Egyptian people know whether they are ready to accept the far more important and expansive demands for democratization, rule of law and economic reform that the protesters (and so many Egyptians) desire.
This is particularly critical since it is the military itself which must continue to play the vital role of holding the nation together, preventing a descent into chaos, fending off more radical elements that seek to hijack the revolution and overseeing a peaceful transition to democracy.
What's more it is a process that will take years to get right, no matter how soon it starts, and the Army will have to remain patient with the trials of a new democracy throughout. While many (myself included) point to Turkey as a rough model, we should all remember that the Turkish military lost patience with democracy too many times in the past during its long transition.
There is another danger lurking, namely that conservative elements within the regime may believe that sacrificing Mubarak will allow them to avoid the wider reforms that the protesters seek. They may well assume that they can make Mubarak their scapegoat, and that the ferocity he has stirred in so many Egyptian souls will be expiated by his departure.
They may believe that his resignation will sate the anger of most Egyptians, who will then lose their interest in the protests and go back to their jobs and their lives, effectively taking the wind out of the sails of the protest movement, and marginalizing the hard core that remain.
After all, those who oppose the protesters have been playing for time ever since their half-baked effort to crush the protests failed. They doubtlessly believe that the protesters and opposition leaders, such as they are, can more easily be dealt with if they have lost the leverage of labor strikes, million-strong marches and the international media attention they bring.
Certainly the strategy of this regime in years past has been to promise modest reforms in times of stress and then to simply fail to deliver when passions cooled and external pressure moved on. No one should assume that Mubarak's resignation will mean the end of opposition from the vestiges of Mubarak's regime. The regime can endure, and those who benefited most from it may well plan to fight on without him.
Thus, the real challenge for the protest movement still lies ahead. Can they maintain popular backing to force the regime to make key concessions on the nature of governance in Egypt, like ending the national emergency laws, establishing a committee to revise the constitution manned by respected opposition leaders, limiting the regime's authority over civil liberties and enacting far-reaching legislation until a new president and parliament can be elected under a new constitution?
If they cannot maintain popular support in the form of continuing demonstrations until they can secure those or other similarly meaningful curbs on the regime's powers, they run a very significant risk of failure.
Mubarak's fall is a great triumph for the Egyptian people, and they have earned their right to celebrate. But it does not signal "mission accomplished." It cannot be the end of their struggles, for if it is, it will also be the end of their dreams.
The opinions expressed in this commentary are solely those of Kenneth Pollack.