The political tone in this country has NOT always been like this. The vitriol in recent years reached levels not seen for many decades.
That said, there is no evidence that the prime suspect had any conventional political motives. He does not seem to have been affiliated with any mainstream left or right wing group and the one racist hate group that Fox News said he liked has claimed that it has no association with him. He appears to be just a very dangerous nut who was able to legally obtain a dangerous weapon and conceal it.