It could happen. A highly motivated vicious 13 % of the population could make a lot of headway against a mostly soft passive unorganized rest of the population. Especially if a large part of the majority population supports the vicious minority until it is too late. There is a process in place right now and moving along pretty fast to undo the official law enforcement capabilities that stand in the way.
Item #1. They are NOT highly motivated...they've shown that through a dozen decades with their work ethic.
Item #2 I think you'll find a large majority of the population DON'T back them...
and Item #3..my favorite..if they manage to undo law enforcement capabilities like they hope...then there will be no one to stop anyone else from shooting them.Or to arrest the shooters after the fact.