"... he explicitly stated his intention to start a race war."

And because in 300,000,000 people there are many hate-filled people, unstable people, and sadly, stupid people in both categories, the easy access to weapons WILL ensure horrible incidents keep happening- perhaps not 'quite' this jaw-dropping or with exactly the same reasoning, but with similar pain, frustration and effects for victims. There is even some evidence that the wide publicity by so many 'news' outlets gives rise to copycat incidents - even as it encourages the sane to do something.,,, and unfortunately, mourning and vigils and fist-shaking are about all that many can deal with.

I am not sure what it would take to get a majority to vote for legislators who will pass relevant laws to make real change.