Of all the crises that threaten to shake Barack Obama's presidency, few are more volatile than the ticking time bomb in Egypt, especially terrifying for the very reason that no one knows when it might explode. Hosni Mubarak, the 81-year-old former Air Force marshal who has ruled Egypt as a police state since 1981, might leave office sooner than anyone is expecting, opening a power vacuum that could send this U.S. ally, its 83 million citizens, and the regional political order spiraling into a fragile and potentially paralyzing tailspin.
 

Or he might not. Mubarak might well linger on for a few more years. Either way, the time bomb will be looming over Egypt for the foreseeable future, and Obama's fortunes in the Middle East will be determined in large part by whether this bomb explodes or gets detonated gently. It's not likely that Mubarak will go down voluntarily. In 2004, he told the Egyptian parliament that he will serve as president "until the last breath in my lungs and the last beat of my heart." Despite incessant rumors of his ill health, he doesn't seem close to those eventualities.

Due to carefully manufactured quirks in the Egyptian Constitution, the most likely candidate to win is the president's son, Gamal Mubarak, turning Egypt into a hereditary republic -- a "republarchy," as Egyptian-American political scientist and exiled dissident Saad Eddin Ibrahim warned in 2000. Gamal might be acceptable to Egypt's business class, but he is not popular. If he assumes the presidency, it could easily trigger a coup, be it an old-fashioned military takeover or a nonviolent "velvet" one that parachutes a senior military officer to the top of the ruling party. The irony of Egypt's predicament is that it is often the self-described democrats of the opposition who advocate such an intervention by the armed forces, thinking that military rule could provide a steppingstone to democracy. Gamal, on the other hand, promises another Mubarak presidency for life.

Throughout this troubled transition, Egyptian initiatives in the region, such as Cairo's attempts to reconcile the Palestinian factions of Fatah and Hamas and its involvement in the Sudanese peace process, would be frozen. Key allies such as the United States and Saudi Arabia, as well as neighbors like Israel, will worry that the situation could take a turn against their interests and might be tempted to interfere. But they'll be working in the dark: The U.S. State Department is ill-prepared for Hosni Mubarak's departure, former officials from George W. Bush's administration say. When the moment does come, U.S. diplomats will be scrambling to understand the fate of their largest Arab ally, one whose ready cooperation has been central to U.S. designs in the region for nearly three decades.

Bad as this all may seem, the alternative could be even uglier: that Mubarak will hang on to power, run for a sixth term in 2011, and go on ruling the country into advanced age. The example of Habib Bourguiba, who remained president of Tunisia for 30 years until he was removed through a "medical coup" at age 84, comes to mind. That may yet be the worst outcome for Egypt: a prolongation of the current uncertainty, with a president increasingly frail and unable to govern -- leading a regime whose moral authority erodes and where centers of powers multiply, with no end in sight.