The shooting of former U.S. President Donald Trump on Saturday was only the most recent act of political violence that has often shaped U.S. history.

Trump said he was "fine” after a bullet grazed his ear during a rally in Butler, Pennsylvania. The attacker was killed by Secret Service agents, and one other person at the event died. Authorities are investigating Saturday’s attack as an assassination attempt.

The killings of Abraham Lincoln, James Garfield and William McKinley eventually led to Secret Service protection, and the assassination of John F. Kennedy shocked the nation and resulted in even tighter security around the president.