The answer to that question, per the Second Amendment, is supposed to be "rise up with your guns in hand and kill them all."

Unfortunately, America's cultural worship of the founding fathers and gun culture has never led it to seriously consider other approaches, as the armed militia was widely considered to be the only necessary bulwark against tyranny, and the only solution that could be trusted. Then it turned out that militia was more than happy to welcome tyranny under certain terms.

So I guess we're just fucked now. ¯\_(ツ)_/¯