After the shocking assassination on former President Donald Trump, any questions still remain about the shooter and the security failures that allowed him to get so close. Six presidents, including Trump, have survived attacks. Four have been killed while in office. Sadly, our history has also full of other notable political figures being targeted from Martin Luther King Jr. and Robert F. Kennedy in the 1960s, to more recent assaults and members of Congress and their families. Over the next hour, CNN's Sara Sidner examines what we now know about the attempt on former President Trump's life, and have these types of attacks have so often changed our country's history.