While mass shootings rose between the 1960s and the 1990s, they actually dropped in the 2000s. And mass killings actually reached their peak in 1929, according to data compiled by Grant Duwe of the Minnesota Department of Corrections. Also, the most common mass murderers kill their own families and acquaintances, not strangers. Either way, such events remain rare in the U.S. All things being equal, the odds of your being killed in a mass shooting are probably no greater than your being struck by lightning.
Moreover, according to experts, the frequency of such tragedies has virtually no significant correlation with what happens in the popular culture, politics or even with gun laws. As James Allen Fox, one of America's leading criminologists, wrote after the Tucson shooting, "Although upgrading the level of political discourse may be much needed and changes in gun laws (whether stricter or more permissive) may be argued, these steps will likely not make a shred of difference in term of the incidence of mass murder."
Floyd Lee Corkins is almost a statistical unicorn in that he (allegedly) made it clear he was politically motivated.
I don't really buy the claim that the political climate has gotten so much worse. But even if it has, that hasn't led to more political violence. Rather, it has led to the politicization of violence. That shouldn't be surprising, given that it's led to the politicization of pretty much everything else as well.
Asymmetrical Politics: Republicans Act Like an Unruly Mob, Democrats Like a Regimented Army | Michael Barone