Regardless of this nutjobs politics, there is no doubt that the rage and threats that have been far too commonplace, are contributing to people going off the rails and acting out the threats and words of others. This goes for both sides, though without question, the most violent threats have come from so-called celebrities, if anyone wants to argue this they can go ahead.
From the top of my head, without any research, I can think of The Colbert Show, Madonna, De Niro, Skinny Snoop Dog video, Griffin, Saturday Night Live, random guys on airplanes verbally abusing the presidents daughter in front of her kids. The list goes on and on.
For the most part, the left attacks have been applauded, reacted by with laughter and it has been mainstream. Some have accepted and celebrated violent words against the president and the GOP. When someone from the Right suggests violent acts, it is generally members of the fringe. All of this on top of a concerted effort to not just insult and make threats, but efforts to usurp the power of the president who was democratically elected. Conspiracies about Russia involvement and ongoing delay and deflect tactics, all of it, contributing to a more angry public.
Rand Paul suggested on CNN that he heard it was political. What that means, who knows. Another said that there was a question asked, he's not sure if it was from the gunmen or not, "are you guys Democrats or Republicans?" Again, very early, I'm just reporting what I'm hearing on the news. Almost certainly, the motive for this is political, unless it's one very extreme random coincidence of terror, as we know for sure, the man planned to go on a rampage.