"We are a player in the Pakistani political system," said Wendy Chamberlin, a former U.S. ambassador to Pakistan, adding that as such, the United States was partly to blame for Musharraf's dip in popularity. But, she added, "This is Pakistan. And Pakistan is a very dangerous and violent place."

That said, Pakistan has never been more important for the United States than it is right now as it teeters on the edge of internal chaos. Bush administration officials have been trying mightily to balance the American insistence that Pakistan remain on the path to democracy and Musharraf's unwillingness to risk unrest that would allow al-Qaida and the Taliban to operate more freely, particularly with American and NATO troops next door in Afghanistan.

That is why the administration had been fighting so hard, amid skepticism from many of its allies, to broker an agreement in which the increasingly unpopular Musharraf would share power with Bhutto after presidential and parliamentary elections. American officials viewed the power-sharing proposal partly as a way to force Musharraf onto a democratic path, and partly to relieve the growing pressure for his ouster.

On the basis of that plan, Bhutto returned to Pakistan in October after eight years of self-imposed exile.

But the power-sharing deal never came to fruition as the increasingly besieged Musharraf imposed a series of autocratic measures, including a declaration of emergency rule and the dismantling of the country's Supreme Court, that left him politically weakened.

Administration officials continued to prod Bhutto toward an arranged marriage with Musharraf even during the emergency rule. Deputy Secretary of State John Negroponte traveled to Pakistan in November and spoke by telephone to Bhutto while Musharraf had her under house arrest. With both sides balking at the power-sharing deal — an agreement one Bush official acknowledged was "like putting two pythons in the same cage" — Negroponte continued to push Bhutto to agree to the plan, according to Pakistani members of Bhutto's political party.

"I think it was insane," said Teresita Schaffer, a Pakistani expert at the Center for Strategic and International Studies, of the proposed arranged alliance. "I don't think Musharraf ever wanted to share power."

Up until this week, Bush administration officials were still hoping that Musharraf and Bhutto would form an alliance between their two political parties after Pakistan's Jan. 8 elections, which would bring about as close to a pro-American governing coalition in Pakistan as the United States was likely to get.

Bhutto's assassination upends that plan, but Bush administration officials on Thursday had still not given up hope that Musharraf may be able to strike a ruling coalition with whoever becomes Bhutto's successor in her Pakistan's People's Party.