I think one sure way to prevent a lot of mentally disturbed people from buying guns would be to electronically link voting machines to the NICS (National Instant Check System).

Any prospective gun purchaser who voted for an extreme anti-gunner like Obama or Hillary Clinton would obviously be admitting to be profoundly insane and mentally ill. You cannot claim to be pro-gun or pro-2nd Amendment if you vote for politicians who wish to infringe upon the gun ownership rights of law abiding citizens. That would be like an abortion doctor claiming to be pro-life.

EDIT: For some reason... as soon as I heard that the shooter was not a Muslim terrorist, but was a whacked-out Liberal Democrat who had been making online rants against Trump... I thought of rocky mtn bill.

Voting for anti-gun Democrats is dumber than giving treats to a dog that shits on a Persian Rug