While I don't think it's just who gets killed, I think there are some groups which would trigger better response than others. Most likely groups:

Republican convention. NRA meeting. Gun shows.

Maybe even a different order... The argument that good people with guns stop bad people with guns would fall pretty quickly after the first real shooting at a gun show. (especially if it results in accidental deaths if someone reacts too quickly and there's loads of people with guns around)