The killing of right-wing activist Charlie Kirk on Wednesday at a college in Utah is the latest in a string of acts of political violence in recent years that have spanned the political spectrum.

Political violence is hardly unprecedented in the United States. In fact, the country has “a long, dark history” of violence that has “struck the highest level of American politics,” said Kevin Boyle, a Northwestern University historian.

After Charlie Kirk’s assassination, Republicans and Democrats on Capitol Hill expressed extreme concern for the state of political discourse in the country.