Tuesday could prove to be a pivotal day in Egypt, as opposition groups call for 1 million protesters to take to the streets, and the world waits for an indication of the army's response.
After three decades of systematic and brutal repression, there is no obvious successor to Mubarak, a challenge that analysts consider cause for both concern and hope.
"You can't talk about the 'secular opposition' because it doesn't exist," says Steven Cook of the Council on Foreign Relations.
Mubarak has ruled under a 30-year state of emergency, barring opposition parties from running against him. Credible opponents have been quashed or co-opted, with some small parties allowed to exist to provide an illusion of political plurality.
There is no charismatic figure in exile, no single jailed dissident who carries the nation's hopes. As analysts try to assess who might emerge to fill a possible political vacuum, the overriding assessment is that it's anyone's guess.
Still, here's a list of some key players to watch:
Grass-Roots Opposition Groups
The protests were originally organized by Internet-based opposition groups, tens of thousands of members strong, who have been laying out their grievances online for several years.
Their calls for strikes and protests had largely fizzled, until the example of Tunisia's uprising lit a fire among Egyptians. Cook, of the Council on Foreign Relations, was in Cairo last week and calls the street protests a "flash mob uprising." There was no leader — they simply happened. Cook says that poses a problem.
He believes the Mubarak regime is "counting on a strategy to sow uncertainty among the population," to instill fear of chaos since there is no other obvious leader.
Nader Hashemi, of the University of Denver, agrees that this is adding to the current confusion, but he also sees a potential long-term benefit. The protests, he says, are "non-ideological. They speak to widespread discontent that exists across social and political classes."
Hashemi says this could prevent one group from consolidating power in the way that Islamists did during Iran's revolution in 1979.
Muslim Brotherhood
Though officially banned, this fundamentalist group is Egypt's largest opposition movement — and once held a sizable number of seats in parliament.
For years, the U.S., Israel and others have worried that in Mubarak's absence, the Brotherhood would convert Egypt into an Islamic regime, reminiscent of Iran's revolution. The group is certainly the most organized opposition movement, able to coordinate through the country's mosques.
The Brotherhood is believed to have the hard-core support of perhaps 20 percent of Egyptians, and some think it could garner 30 percent or 35 percent of the vote in open elections. But Hashemi says this depends on the alternative.
"If you open up the political spectrum," he says, "you'll see support for the Muslim Brotherhood diminish."
Hashemi also believes the Brotherhood today looks less to Iran as a model than to Turkey, where a moderate government has presided over a vibrant democracy and strong economy. The Brotherhood claims among its ranks academics and others who support a secular government.
The Brotherhood was cautious in its initial approach to the current demonstrations, though its members have been increasingly evident at the protests in recent days. The group has joined others coalescing behind Nobel laureate and opposition figure Mohamed ElBaradei. But Cook says that could change.
"Historically, they've only sought to cooperate with others when they felt it necessary for their own survival," he says. "In the event the state collapses, maybe they won't feel that need to be in a coalition."
Mohammed ElBaradei
The Nobel laureate and former head of the International Atomic Energy Agency, the U.N. nuclear watchdog group, began frequent trips back to Egypt from his longtime home in Vienna last year with an aim to foment opposition to the Mubarak regime. A coalition of opposition groups has coalesced around him, calling themselves the National Coalition for Change.
"What ElBaradei has succeeded at is articulating an agenda that a lot of Egyptians could support," says Michele Dunne, of the Carnegie Endowment for International Peace and a co-chair of the Working Group on Egypt.
Hashemi, of the University of Denver, says ElBaradei is seen as a neutral compromise figure, and could play an important role in any political transition. Still, ElBaradei hasn't explicitly said he would stand in elections if they were held, and it's not clear how much support he would garner.
"He's more well-known outside Egypt than inside," Hashemi says.
Omar Suleiman
Suleiman's recent appointment as vice president was the first sign that President Mubarak may intend to concede power, but few believe this key Mubarak ally can play anything but a transitional role, if that. He is close to the army, and could prove pivotal as the dance between soldiers and protesters plays out in the streets.
But as a longtime former director of intelligence, "Frankly he's associated with human rights abuses, with widespread torture," Dunne says.
For him to survive as a transitional leader, she says, would depend on what promises he might make: a constitutional change to allow opposition? Free elections by a specified date?
On the other hand, Cook says he can imagine Suleiman declaring a continued state of emergency and trying to put off elections now scheduled for September.
Ayman Nour
In 2005, Nour was the first true opposition figure allowed to contest elections, a move seen as a bow to pressure from the Bush administration. The official results gave him 12 percent of the vote, though the vote was not considered free and fair.
Shortly after, Nour was tried on trumped-up charges and sentenced to five years in prison. He was released in 2009.
The Mubarak regime "worked hard and somewhat successfully at besmirching his reputation," Dunne says. "But I do think he gets a certain amount of begrudging admiration from people in Egypt for the fact that he was targeted by the regime over many years and never abandoned his principles."
Still, whether Nour can reorganize his political party, El Ghad, and foster a broad base of support remains to be seen.
