They aren't invading. That's too costly. They're just helping us tear ourselves apart from within. We're literally doing the dirty work for them. All the guns in the world aren't going to change that. By the time we're done we'll probably welcome them with open arms (POTUS practically does).
Guns aren't legal to protect you from your own government. That's still treason. They're legal for arming militias against foreign invasion. (It's like they only read the parts of the constitution they like. Kinda like the bible.)