Amid all the media frenzy around the Nigerian underwear bomber and how America should have stopped him before he tried to blow up a passenger plane on Christmas Day, a critical piece to the counter-terrorism puzzle seems to have been missed: where in the world is the Nigerian President?

Normally, after such a horrific incident, President Obama would be on the phone with his counterpart, discussing what went wrong and agreeing on ways to work better in the future to prevent such attacks.  But this couldn't happen because Nigeria's President Umaru Yar'Adua left his country for medical treatment in Saudi Arabia on November 23rd and hasn't been seen or heard from since.

Yes, you read that right:  the whereabouts of the leader of Nigeria—America's most important strategic ally in Africa, the fifth largest source of U.S. oil imports, and home to 150 million people—are unknown. It is also not clear if he is alive or dead.

The situation is so uncertain that Nigeria's parliament is openly considering sending a delegation to Saudi Arabia to find out the truth. A major opposition party yesterday demanded, quite reasonably, some "proof of life".

The mystery over Yar'Adua is so bizarre as to be comical — if the consequences weren't so severe. His absence has thrust the country into an immediate constitutional crisis. The President failed to delegate authority to his deputy before travelling, effectively leaving no one in charge. This 43-days-and-counting power vacuum is being swiftly filled by an insular cabal bent on exploiting the situation for their own gain.

Complicating matters, the vice president— ironically named Goodluck Jonathan — is a Christian and an Ijaw, part of a minority group from the southern Niger Delta region and far from the power centers of the northern Muslim elites who expect one of their own to run the country. There is much speculation that insiders are scheming now of ways to keep Jonathan from ever assuming power. In an ominous sign, a new chief justice was quickly (and possibly illegally) sworn in last week.

These developments all put Nigeria's future at great risk. A decade of constitutional democracy is threatened by the specter of mass violence and a possible military coup.

The failed terrorist attack by Umar Farouk Abdulmutallab on Northwest Flight 253 highlights that Nigeria's power void is dangerous for the U.S. as well. The foundation of a counter-terrorism strategy is to build cooperative partnerships with friendly nations. This means sharing information and helping to build security capacity in places like Yemen, Afghanistan, and Nigeria.

But we cannot have a partnership if there is no one on the other end of the line. Nigeria cannot be a reliable ally if it is consumed by its own corruption and political machinations. In this way, Nigeria is rapidly becoming more like Somalia— a failed state with no real government to cooperate with— than a real partner.

What can the United States do? First, it should insist on an immediate public declaration of President Yar'Adua's health and fitness to govern. If the President's staff refuse to oblige, then the U.S. should encourage the national assembly to assert its constitutional responsibilities when it reconvenes on January 12.

Second, if, as seems likely, Yar'Adua is in fact incapacitated, the U.S. must demand that the constitution be followed and power transferred to the vice president. The long-term security of Nigeria depends on entrenching the rule of law and this must supersede any palace intrigue or political bargaining.

Third, it is clear that whatever the outcome over the next few weeks, Nigeria will remain on a knife's edge until elections in 2011.  Any hope for a more stable country hinges on a credible election next year. Yar'Adua came to power in a deeply flawed poll in April 2007 and almost no steps have since been taken to fix the broken system. The U.S. is in a unique position to push for and help deliver a better election that would strengthen the authority and legitimacy of the next government.

Last, the U.S. can support Nigeria's vibrant civil society that is clearly fed up and is increasingly demanding change.

The case of the missing Nigerian President is a wake up call to the United States about the vulnerability of many of our global partners. How we respond is not only crucial to the future of an important ally, but a critical test of our strategy for building partnerships in troubled places to combat the global ills of our time.

Todd Moss is vice president and senior fellow at the Center for Global Development in Washington DC. He served as Deputy Assistant Secretary of State for African Affairs during the Bush administration.