Only a few details about accused killer Jared Lee Loughner have come to light. It seems that he was declined enlistment to the Army due to suspected drug use, although that isn’t confirmed yet. Also, Loughner’s targeting of Giffords apparently goes back to some contact he had with her in 2007 — before the Tea Party, and before Obama.
So it’s not possible to draw a direct line between the toxic political tone of the times, and what Loughner allegedly did. However, I’ve seen video of Giffords back in March saying that she was concerned about Sarah Palin putting crosshairs on Democratic districts. Based on that, Palin’s PAC was aware of how the map was perceived, and yet left it in place.