The only people who have any power in the country right now are the military. Fujimori clearly no longer holds the reins, and the opposition leader Alejandro Toledo has no power at all. The congress has been completely discredited by the video that launched the current scandal, which shows Montesinos bribing an opposition legislator into joining the government. So that leaves the military as the only real authority in Peru right now. And the military haven't said whether they'll back Montesinos or Fujimori. Remember, almost all of the senior commanders in the military were put there by Montesinos, and three quarters of them had been his old classmates.
Many Peruvians think that what's going on in the barracks right now is a race to see who'll be first to actually pull off a coup. Montesinos's appointees might decide to sacrifice their patron but save their own skins by launching their own coup. Or the mid-level officers who've had enough of what's going on could simply revolt. So far there's no sign of any unusual troop movements, but people believe there's no way out of the political impasse and that might make the generals think a coup is the only solution.