Having had discussions with a guy who used the, "Pro-Lifers' rhetoric causes violence," shtick rather promiscuously, I'm reluctant to use that sort of line. That said, one of the posts on the link I just posted had a reminder about a professor's Tweet saying R Congress-Critters who voted to repeal OhBummer!Care should be "lined up and shot". The there's Kathy Griffin and that butchered version of "Julius Caesar". So I think that narrative is an appropriate question to ask - the Hate-Trump rhetoric has been that vile and violent.
The shooter may turn out to be a fruitcake with no coherent political thoughts. Similarly, the shooter may turn out to be a white supremacist who is disappointed that Trump isn't the racist the shooter hoped Trump would be. He might even be John Hinkley. So I'm ready to wait for facts to become known.