Amr Moussa, Arab League secretary-general, went to Tahrir Square to support the protests. The crowd cheered him. This is a symbol that the current government is sinking but also a sign of what the next regime may become.

It appears to be sinking, indeed. But Moussa represents the worst demagogic forces of radical Arab nationalism. Syria, Moussa, and other forces in the Arab world represent that radical wing, while Mubarak followed policies that might be deemed more moderate and Egypt-centered. And as brutally repressive as Mubarak's regime was, Syria and Iraq -- radical regimes -- were worse.

Let's be clear: young Facebook users are not the entire population of Egypt. Let's speculate about the political blocs that might emerge in a post-Mubarak Egypt.

"Establishment" Reformers: Muhammad ElBaradei has been practically coronated by foreign observers yet his appeal is untested and his organization almost non-existent. One of the most important "secrets" of Egypt today is the degree of his dependence on the Brotherhood. Indeed, of all the possible opposition candidates he is about the closest to the Brotherhood. That's no coincidence: that's precisely why he has flourished. And the Brotherhood will run on a joint ticket with him. If he has no strong opponent he will win the presidency and his party will be the largest in parliament.

"Good Government" Reformers: A small party (or parties) of honest true advocates for true democracy. These are the young people out demonstrating who have carried the weight of the revolution so far. But how many votes would they get? Very few. That's the difference between a demonstration, even of tens of thousands of people, and voting by tens of millions of people.

The Regime Supporters: This is a big question mark. The ruling NDP, even if it changes its name or appears in a totally new guise, could get anywhere from 0 to 25 percent. It seems unlikely now that it could be a factor but even old Communist parties have made comebacks in the ex-Soviet bloc.

The Left: Quasi-Marxists and extreme nationalists who may fragment or produce a joint ticket. They might get 5 to 10 percent.

But suppose Egyptians don't want the Brotherhood and they band together to support a secular candidate, who might win the presidential election? That brings us back to Moussa. He's far more popular than ElBaradei, knows how to be a demagogue, is familiar and seems more of a known quantity, and is anti-Israel and anti-American enough to galvanize the masses.

The problem is that both outcomes are bad: with ElBaradei you get the possibility of growing Islamism; with Moussa there is an updated form of radical Arab nationalism.

In either case, the Muslim Brotherhood will not take power and Egypt will not become an Islamist state overnight.

The Brotherhood is not stupid. While wealthy, secularized, urban Egyptians may look at them as a peasant rabble, this group has maneuvered very skillfully in the past. Does it have different factions and tendencies? Certainly it does. Yet it is going to be more united than any other political factor.

My concern, at least for the next three years, is not an Islamist Egypt but a radical Egypt. The idea of a "Turkish model" has been raised, that is an Islamist party in power that advances very slowly but steadily toward the goal. Such a government, however, would show itself most clearly in foreign policy, which is what other countries are most concerned with, of course.

Yet if Moussa wins there will also be a radical Egypt, closer to what existed in past decades before Mubarak, and before him Anwar al-Sadat, came to power.

Either way a post-regime Egypt is likely to move closer to Syria and Hamas, not Saudi Arabia and Jordan. It will not be a good friend to Iran but not very interested in combating its influence. Terrorists, as long as they had other targets in mind, would pass freely through Egypt under the Muslim Brotherhood's protection or the regime's indifference.

Will the Egypt-Gaza Strip border be opened up? As with all potential dangers we are told there is nothing to worry about. The new regime would not want to make Israel angry, lose U.S. aid, or defy the Egyptian army. But really, would the Obama Administration cut off aid if Egypt opened the border for everything, including weapons? ElBaradei has said he would end the blockade; Moussa would certainly do so.

And is the army going to be the bulwark of democracy in a new Egypt, Turkish style? Well, if the new republic is going to go to a coup we may be back in 1952, which is how the regime got started in the first place. But in discussing the army's role, observers are missing a key point.

It is conceivable that if the Muslim Brotherhood were going to take over the government altogether and make Egypt an Islamist republic, the army would take action. But that does not apply to a radical nationalist Egypt, with which many officers would sympathize, or even an ElBaradei government in which he maintained the army's budget and left it alone.

They would accept a turn away from America (in which Egypt, like Turkey, could avoid any actual bilateral trouble with Washington); a high degree of hostility toward Israel; support for Hamas as long as it stays off Egyptian territory; and alignment with radical forces elsewhere, at least if they are Sunni.

Along with the Turkish model, there's a pattern attractive to Egyptian Islamists: the Lebanese model. Hezb'allah, for all practical purposes, is running Lebanon today. But it is doing so behind a screen of non-Islamist politicians and many political alliances.

Of course, Hezb'allah has the advantage of help from Iran and Syria. Yet in Lebanon the Shia Muslims who form Hezb'allah's base are only 30 percent of the population. In Egypt, Sunni Muslims are 85 to 90 percent. Of course, many of them -- probably a majority -- would never support the Brotherhood, yet the Brotherhood's political base constitutes alone about the same size as Hezb'allah's direct support.

And even that is an underestimate because the Brotherhood will be cautious and try to rule through others, notably ElBaradei.

Once again, the problem is not an Islamist Egypt in a year or two but a radical Egypt that will wreak havoc on regional politics. At home, the new government would face dreadful economic problems without a way to deliver higher living standards. That's a formula for instability, demagoguery, and foreign adventure.

One can also expect the development of small Islamist terrorist groups, coming out of the Brotherhood's impatient hardliners, as happened in the 1990s, to assassinate secular or moderate figures and to attack Christians and possibly tourists.

Certainly, I hope I am completely wrong and Egypt becomes a stable moderate republic .at peace with its neighbors and making its people happy and prosperous. But, as the Oslo process and Iranian revolution -- among other historical events -- have taught, letting one's hopes determine one's judgment is the road to disaster.

Professor Barry Rubin, Director, Global Research in International Affairs (GLORIA) Center; The Rubin Report blog; Editor, Middle East Review of International Affairs (MERIA) Journal;  Editor, Turkish Studies.