Would the US stand for something like that? During the Cold War anything that even looks in the general direction of communism is getting stepped on hard, even after the USSR collapses the fact that they're probably funding themselves with drugs and expropriating foreign owned businesses (a lot of whom would probably be owned by US interests) it's going to see them heavily supporting the government against them.
Before the cold War, the Us would have tried to do something against them. But if it happens in the early 1990is, let's say, in 1991/1992, the US might be more concerned about what's happening elsewhere (Iraq, Eastern Europe, Russia) to care much. And, after all, it's not that they'd be a base for Russian submarines or missils. Unless they try to establish a close alliance with Chine, and invite Chinese troops in (which is something the Chinese wouldn't accept anyways, not in those years) they may probably be more or less alone. At most the US would support neighbouring countries (Bolivia, Ecuador, Colombia and Chile) and back up any internal oppossition that arrises in Peru.