The United States has full knowledge about the location of Pakistan's nuclear weapons, according to the U.S. assessment.
But the key questions, officials say, are what would happen and who would control the weapons in the hours after any change in government in case Musharraf were killed or overthrown.
Musharraf controls the loyalty of the commanders and senior officials in charge of the nuclear program, but those loyalties could shift at any point, officials say.
The United States is not certain who might start controlling nuclear launch codes and weapons if that shift in power were to happen.
There is also a growing understanding according to the U.S. analysis that Musharraf's control over the military remains limited to certain top commanders and units, raising worries about whether he can maintain control over the long term.
This does not inspire confidence.
