This is a possibility because the vast majority of federal troops could no longer be persuaded to open fire on Americans. Federal law enforcement absolutely, the vast majority of the army and marine corps no way. And if pressed to do so there is a good chance that many would simply change sides bringing their arms and equipment with them. Many things could trigger such a movement including gun bans, a defacto ban on opposition media, the growing domination of all 50 states by a handful of states, and/or a national economic collapse.
The political collapse will happen when the military is sent to bring arms agains US citizens to impose some unconstitutional law on a large scale. A large (heavily armed) part will refuse, setting up a battle (figuratively if not literally) between federal law enforcement and their loyalists vs. the rest of the military and irregulars.