There are something like 100 million gun owners in the US, including millions of veterans of the military and law enforcement with equal skill sets to those serving.

Even if every serving military member and every law enforcement officer in the US decided to back some sort of tyranny, that is about 2 million people total, not the useful combat arms or street cops, a much smaller number, but total.

They and their families all live and work amidst the same people they would be "oppressing," meaning that the most potent weapons could not be used without risk to their own loved ones, and they and those loved ones (and all their possessions) would be vulnerable to individual retaliation. They would also be having to defend the nation and fight "normal" crime at the same time.

Anyway, the extant facts mean that only an idiot would actually try to seriously circumvent the 2nd Amendment rights of gun-owning Americans -as even a minority view them-,  because "the government" would lose.