Could you imagine that an actual revolution which would coup the government could actually happen in modern day America?
Short answer: no. An armed or typical revolution would be put down with ease.
Longer answer: never say never.
It's important to realize that any system is composed of people, with all of the weaknesses and blindspots that entails. This includes government, the military, and our intelligence community. The continuity and function of our government is determined by less than 2,000 people: 535 Members of Congress and a handful of their aides, the President, White House and its staff, the military leadership, and a handful of influential governors and business leaders. Hell, some corporations are more complex than that.
If you can effectively exploit the vulnerabilities and blindspots of even a small fraction of these 2,000 folks, you can effectively wield power in this country. You can raise hell or get a lot of good things done; it's up to you.
Someone exploiting these vulnerabilities at a point of great national distress - war, economic depression, or some calamity - could effectively wrestle functional power away from the government, especially if combined with some armed revolution. It can happen anywhere. Kind of a scary thought, eh?