A white metal roof over a beige hangar was added to the list of emblematic sites of political violence in the United States on Saturday, July 13. From that building, home to the consulting laboratory American Glass Research, shots were fired targeting Donald Trump at the start of the rally he was holding less than 140 yards away, on the agricultural fairgrounds of Butler, a rural town in Pennsylvania with a population 13,500.

The attack immediately joined the country's collective consciousness, especially since it was filmed live. Although the former president escaped safely, the white roof on which the gunman stood is likely to be long remembered, like Dealey Plaza, in Dallas, Texas, where President John F. Kennedy was killed on November 22, 1963, by a gunman ambushed from the top floor of the school book depository. Similarly, there is the balcony of the Lorraine Motel in Memphis, Tennessee, where Martin Luther King was shot dead on April 4, 1968, by a right-wing extremist. Or the kitchen of the Ambassador Hotel in Los Angeles, through which Robert F. Kennedy was walking on June 5, 1968, after a victory speech in the California Democratic primary, where a Palestinian-Jordanian man opened fire. Or the Hilton Hotel in Washington, where Ronald Reagan was shot and seriously injured on March 30, 1981, 90 days after his inauguration, by a disturbed man seeking the attention of actress Jodie Foster.

Political violence is "bred in the bone" of the country, observed former Richard Nixon Presidential Library director Tim Naftali on CNN. "It's something we ought to remember − we are capable of this as a nation." Since the founding of the US, four presidents have been assassinated. In addition to John Kennedy, they were Abraham Lincoln at the end of the Civil War in 1865, James A. Garfield in 1881 and William McKinley in 1901, at a time of extreme divisions between progressives, radicals and conservatives, comparable to today's antagonisms.

Six other presidents have been the target of assassination attempts: Andrew Jackson in 1835, Theodore Roosevelt in 1912, Franklin D. Roosevelt in 1933, Harry S. Truman in 1950, Gerald Ford in 1975 and Ronald Reagan in 1981. When Theodore Roosevelt was shot in the torso in Milwaukee, Wisconsin, he was seeking re-election after his first term in the White House. Despite the injury, he continued his speech before being taken to hospital. Many Republicans today draw parallels with Trump's defiant, fist-raising stance before being evacuated by the Secret Service. However, they often forget that Roosevelt was defeated by the interventionist Democrat Woodrow Wilson.

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