1) anything that can be called an "assassination" is inherently political;
2) very often the "politics" are obscure, personal, or reflecting mental disorders rather than "normal" political disagreements. But now a further step,
3) the political tone of an era can have some bearing on violent events. The Jonestown/Ryan and Fromme/Ford shootings had no detectable source in deeper political disagreements of that era. But the anti-JFK hate-rhetoric in Dallas before his visit was so intense that for decades some people debated whether the city was somehow "responsible" for the killing. (Even given that Oswald was an outlier in all ways.)
I still stand by much of what I said before. Republican rhetoric of the past two years have been overheated and fantastical. We should not be surprised, then, when a man with a tenuous grip on reality should react to the unreal and hysterical climate with violence. Crazy ideas make crazy people do crazy things.
They also coarsen the lucid:
I hear one of the women say, “Well, that’s to be expected when you’re so liberal.”
And the other woman says, “Ohh, so we get to appoint a Republican?”
In any case, Giffords had already had a rock hurled through her office window, and a handgun brought to one of her town hall events. I can't speak to the mental well-being of the perpetrators in those cases, but I also don't think it wise for Republicans and Tea Party groups to wait to change their rhetoric until someone is directly harmed because of it.