There's no doubt that Dylann Roof was influenced by white supremacist thugs, but when he murdered those 9 prayer-meeting attendees in June 2015, "Trump Fascists" were barely on anyone's radar. Roof had plenty of local idiots to copy without looking to someone from New York.
The "ultra-partisanization" of US politics began, IMO, with the GOP reaction to Bill Clinton's election in 1992, then the Dems upped the ante after their 1994 losses by initiating the endless campaign. Since then, I don't think there's been a single day that I did not see/hear political attack ads. except when I've avoided subjecting myself to mainstream media.