America goes through a bloodless revolution every so often; we call them elections. The American public has the power to vote in or out whichever candidate they so choice. While it doesn't mean that our senators/representatives/etc always do what's in their constituents' best interest, it doesn't mean that we as a people don't have power over them. And for the politicians that don't follow the ideal that their offices represent, they tend to be swayed by public outcry.
Of course, The Public would need to be well informed to do that, but that's a topic for another day.