I'll steer well away from debating about gun control, but I'd like to point out the fact that it was an incident like today's which spurred Texas to allow people to carry concealed weapons several years ago.
A crazy man drove his pickup through the front windows of a Luby's restaurant and started methodically executing the patrons there. A woman who was skilled with guns was eating at the restaurant with her elderly parents. Her gun was in her car outside, but if concealed carry had been permitted, she likely would have had it in her purse, and likely could have easily taken out the gunman. She could do nothing, though, and both her parents were killed.
She became the most vociferous proponent of allowing concealed carry permits in Texas, and it probably would not have passed without her efforts.
Again, I am not wanting to debate, especially since I don't have a strong opinion either way, but I think it's an interesting, and surprising, history lesson about the effects of these kinds of tragedies on politics.