The government can't really do that much to improve human rights, but they can do a lot to curtail them. The funny thing is that, while there are a lot of problems I'll get into later, the US is one of the best countries in the world when it comes to your rights against the local policeman. You have every legal right to say nothing to them other than maybe presenting your identification, you have every legal right to deny them a search unless they have a warrant, and once you're in custody, you have every legal right to shut your mouth and say nothing, and they aren't even allowed to beat you up. Any evidence that is gathered in violation of a person's civil rights is thrown out in court. Add in the freedom to express any political viewpoint whatsoever without worrying about violating some vague "hate crimes" laws and the constitutional right to own firearms, and we're at a point that most European countries would say is outright excessive in terms of personal freedom.
As I mentioned though, I don't want to whitewash the US record. Police abuses do happen far too often, the TSA is an obnoxious joke, and asset forfeiture is a very problematic principle. The FBI, CIA, and NSA can in theory do nasty things to you, but they can do nasty things to you whether or not you're American. Plus, once you've gone through the due process, the prisons are pretty fucking awful and you have to stay there for an excessive period of time. And we have a death penalty. And the drug laws are a joke.