How sick is President Yar’Adua of Nigeria? In May, he admitted during a live television broadcast that he suffers from a kidney ailment, but sought to quell speculation that he was terminally ill by insisting that fears for his health are greatly exaggerated and politically motivated. There are plenty of world leaders in less-than-perfect health. But the stakes are especially high in Nigeria, where Mr. Yar’Adua embodies the country’s delicate political balance.

With the fall of Nigeria’s dictatorship and the introduction of democracy in 1999, governors in the mainly Muslim northern provinces believed they had struck a deal with their southern counterparts on a regional rotation of the country’s presidency. In 2007, arguing that it was their turn to choose a chief executive, they bitterly opposed a bid by the president at the time, Olusegun Obasanjo, a southerner and a Christian, to rewrite Nigeria’s constitution in hopes of winning a third term. Southern governors countered that the north had controlled the country through more than three decades of authoritarian rule and that a southerner should hold the presidency for years to come. Tensions mounted.

Once it became clear that his gambit would fail, Mr. Obasanjo found a compromise: he named a man he trusted, Mr. Yar’Adua, a little-known northern governor and devout Muslim, as his preferred successor. In April 2007, Mr. Yar’Adua won a disputed landslide presidential victory. Western and African observers charged that widespread vote-rigging had tainted the official result, and Nigeria’s Supreme Court has yet to rule on challenges to the election’s legality.

But Mr. Yar’Adua shrugged off charges of electoral fraud, and in the first days of his presidency, he drew praise, both at home and abroad, for promises to tackle corruption and pursue an agreement with militia groups in the oil-rich, violence-plagued Niger Delta region. In reaching out to armed groups like the Movement for Emancipation of the Niger Delta, one of his primary assets has been his vice president, Goodluck Jonathan, a native of the area.

Pacifying the Delta is vitally important, because Nigeria, the world’s eighth-largest oil producer, earns 86% of its export revenue from oil. Attacks on pipelines have recently intensified ahead of a planned summit meeting between the government and various militia leaders, as small groups of militants stage attacks on oil infrastructure in the Delta to establish their relevance and win a potentially lucrative seat at the negotiating table. The summit is likely to generate an agreement and positive press coverage, but northern Muslim members of parliament could complicate efforts to implement the deal.

The Nigerian government could use some good news. Electricity shortages have intensified on Mr. Yar’Adua’s watch, producing blackouts in many areas of the country and darkening the foreign investment climate. Rising food and energy prices pushed inflation up to 9.7% in May from 8.2% in April. Corruption investigations launched by Mr. Yar’Adua’s government have uncovered broader and deeper problems than many knew existed. A battle between the president and legislature over control of federal spending has not been fully resolved.

For foreign investors, the greatest near-term concern may be a broad range of attacks from parliament and some of Mr. Yar’Adua’s economic advisors on the central bank governor, Charles Soludo, who is widely credited for Nigeria’s improved economic performance in the past several years. Under Mr. Obasanjo, Mr. Soludo initiated much needed banking reforms and argued strenuously that Nigeria should pay its foreign debt.

But Mr. Soludo’s recent decision to create a sovereign wealth fund has ignited a firestorm. Lawmakers complain they weren’t consulted. Northern Muslims wonder why Mr. Soludo, a southern Christian, believes the government should horde excess cash that could be spent to relieve poverty among their constituents. A favorite of the West, Mr. Soludo may not survive the year.

With so many challenges ahead, Nigeria can ill afford an ailing president. Mr. Yar’Adua insists that he’s fine and that his trips to Germany for medical treatment, during the election campaign last year and again this April, have been unfairly politicized. But there are plenty of unanswered questions about his kidney condition and speculation that he may even have Churg-Strauss Syndrome, a life-threatening autoimmune disease. The true state of his health may matter less than public fears that he’s hiding something.

Mr. Yar’Adua’s health worries are creating risks to Nigeria’s stability that run far beyond questions about the Niger Delta or any single political issue. If Mr. Yar’Adua were to die in office, his vice president would succeed him — returning the presidency to a southern Christian. Nigeria’s northern Muslims are highly unlikely to accept that result without protest.

There is no reason to believe that Mr. Jonathan will preemptively resign, and removing him from office if he assumes the presidency might well stoke unprecedented violence in the Delta. Given the political friction and violence generated by last year’s election campaign, new balloting would prove a less-than-appealing prospect.

Only Mr. Yar’Adua’s doctors know for sure how sick he is. But as answers begin to emerge, we will learn much more about the health of Nigeria’s fragile democracy.

Mr. Bremmer is president of Eurasia Group and a senior fellow at the World Policy Institute. © 2008 Project Syndicate