The resistance, if there were one, wouldn't be against the Army and Air Force, it would be against law enforcement agencies. But even then, the track record of armed resistance against law enforcement is simply putrid.
As for making it impossible for the regime to maintain any semblance of humanity while putting large groups of people down, it's the 1st Amendment and not the 2nd that protects our liberties. The proliferation of cell phone cameras and the ability to upload and livestream video has been 1,000,000x more effective than any number of guns. Until then, the government could oppress, suppress, and outright murder almost anyone it wanted. There's a video I saw on YouTube several years ago, of Malcolm X on Dick Cavett's show, talking about how NYPD officers could and would come into Harlem and do basically anything they wanted to the people there, and it wasn't until relatively recently that we can all see that he was right. And I hadn't even heard of the 1921 Tulsa Massacre until it was featured in an episode of Watchmen. The Edmund Pettis Bridge 1965 is pretty famous, but I wonder how many people today know about Kent State 1970? If such a thing happened today, it wouldn't be AR-15s that would protect and/or avenge the victims and expose the perpetrators, it would be iPhones. And this isn't hypothetical. We've see it already. During the demonstrations/riots/uprising in Ferguson, MO after the death of Michael Brown in 2014, I remember seeing a police officer on-camera pointing his shotgun at peaceful, albeit angry, demonstrators. You could see on his face the officer was terrified and furious and didn't know what to do. The police also deployed armored cars and snipers, again, all on camera. To my recollection, none of them fired. None of them has said so - and they wouldn't, would they? - but I'm sure it was because they were on camera and the whole country was watching.