On We Are Respectable Negroes, Chauncey DeVega considers whether a military coup could occur here, and finds the question to be not at all hypothetical:
I have mentioned this essay from Harper's a few times here on WARN. I assign it in my introductory American Politics courses as a way of getting students to think about our country's cultural, social, and political institutions. Could there be a military coup in the United States? What would it take to be successful? Would the officer class go along with it? What of the average rank-and-file soldiers?
My answer has always been as follows: why does the military need to have a coup when they effectively run the show anyway? Moreover, the United States is a thoroughly militarized society from the bottom up (and has only seen the walls between the military and civilian life become thinner and thinner with the post-Cold War up-gunning of local police departments, and Patriot Act national security era).