I've no idea why this nutjob killed 12 people. Was it lax gun laws or a dx on the spectrum? Or something else that someone can and will blame? But I do know that these things happen more frequently overseas, per capita. Seems to me that the 2d amendment doesn't protect the people. Happening one tragedy at a time, too.
Say that a real nutjob becomes president, nut only some half nutjob like G.W. Bush, but someone absolutely batshit insane person, and that he starts putting Americans in concentration camps etc. The Americans then by far have better opportunities than most Europeans, maybe with the exception of Switzerland and the Czech Republic.
They can't win battles against the US armed forces, of course, but they can carry out acts of sabotage and kill high officers, officials, politicians etc. as acts of resistance.
In countries like China people don't have guns, so they can't put up any resistance to start with. In countries with guns but with strict gun control, they know who has legal guns and, in case of severe resistance, they shoot the gun owners first. When the Germans occupied France, the French had 24 hours after the French capitulation to give up their private guns to the German military. When Germany itself was defeated, no German civilians were allowed to own guns again before 1956.
The fact that the military confiscated guns from civilians as well shows that it's not pointless to have civilian guns as a last resort of resistance. If they really had believed what the proponents of gun control are saying, that you don't stand a chance with civilian guns, why, then were civilian guns confiscated?
In Yugoslavia everyone had guns in the 1930's. Yugoslavia was also extremely hard to keep occupied during WWII. It's also believed that one of the reasons that Switzerland was never invaded, despite it being a country with a German majority (and thus "belonging" to Germany), was that every Swiss male had a gun. Same reason why the Japanese never tried to invade the US mainland. They knew that not only the military but most civilians too would be able to defend themselves.