One thing to add to Doyle McManus' excellent piece on Republicans in Congress finally turning away from the Grover Norquist pledge never to increase taxes: Norquist has been clear about his reason for demanding that promise. He's on record advocating lowering tax revenue to, in his words, "reduce [government] to the size where I can drag it into the bathroom and drown it in the bathtub."
In 1949, 11 members of the American Communist Party were tried in New York City, not for a specific plan to overthrow the U.S. government by force but for a "philosophy" of violently overthrowing governments. They were found guilty and sentenced to jail terms.
If drowning our government in a bathtub isn't a description of a planned violent overthrow of the U.S. government, I don't know what is.