I'm feeling angry and upset about the mass killing in Orlando. My earlier, more hyperbolic title was, "Does your Senator support Terrorism?" but I've edited it to something more precise.
You can call, e-mail, or write your senators with this link, or find your congressperson here.
An assault weapons ban wouldn't affect most murders in the US, but it would be a good start. Here's a nice article by Adam Gopnik that suggests other sensible gun control steps.
Information on the 2013 assault weapons bill is here or here.