Do I write my congressman?
Yes
Eta: also, vote out all the politicians beholden to the NRA, and not to the safety of your kids.
these things.
The fact that schools nowadays have lock down drills for active shooter scenarios is.....insane. 
Youshould see the ALICE drills that my wife, a kindergarten teacher, and her colleagues have to endure. They instruct them how to barricade against and defend against active shooters. It involves police officers forcibly entering their classrooms and “killing” them with a yardstick. Horrifying for anyone. Now imagine them instructing her how to teach 5 year olds to go on the offensive in last ditch efforts. This whole situation is unimaginable, but here we are.
I admit, I just had to look up ALICE drills, and didn't even know these drills existed until this weekend. How fucking insane is that this is the world we live in today? And talk about mental illness...you think this isn't contributing to an entire generation of kids growing up with some level of PTSD, and/or constant state of fear that something like this could happen in their schools, wtf! And I KNOW I can't be the only one that has had that thought run across my mind, even in passing, while at a concert, or a movie theater, or a crowded festival or outdoor event, that some shit like that could go down. It might be an irrational fear, and infinitesimally small chance of ever occurring, but I'd be lying if I said I've never thought that. And you got kids growing up with that kind of shit?

MAGA! 'Murica!