Believe it or not 4 out of the last 30 Presidents were assassinated, an additional 3 were shot, and a few more were shot at or otherwise survived attempts. There's a long history of political violence in the US (and the world). We've been in a bit of a lull of late but what we're experiencing today is not all that abnormal.

Why is your sample size 75% of US history? 30 presidents is a huge number to start with.

I mean the sitting president was shot on the campaign trail.