text:  This is All Things Considered from NPR News. I'm Elsa Chang. And I'm Juana Summers. The assassination attempt on former President Donald Trump marks one of the most serious incidents of political violence in the U.S. in recent memory. As NPR's Sarah McCammon reports, it also calls to mind similar moments in the past when democracy seemed to be under threat. Historians tend to be a bit cautious about drawing too close of a comparison between the present and the past. What we tell people is that