The violent rhetoric need not directly incite those like the Tucson shooter to make such events more likely.
In a culture boiling with tough-talking dipshits, the truly dangerous don't stand out enough to attract attention and intervention until it's too late.
This is simple common sense.
A few years ago, if someone showed up at a republican political event carrying a gun, he would be treated like threat he is, instead of ignored until he starts shooting.
To borrow one of Palin's favorite jokes...
How do you tell the difference between a crazed assassin and a political demagogue?
Lipstick.