One spectator was killed and two others critically injured in the attack, which took place at the Butler Farm Show in Butler City.

The Secret Service says its personnel killed the suspected attacker, identified as Thomas Matthew Crooks, 20, from Pennsylvania.

Since the founding of the US, four presidents and one presidential candidate have been assassinated.

These are some instances where US presidents and leading presidential candidates were targeted in assassination attempts.

• 1865, Abraham Lincoln (16th president) – Assassinated while watching a theatre play with his wife in Washington, DC. He was shot by John Wilkes Booth and was given medical treatment, but died the next morning. Booth was found hiding in a barn in Virginia 12 days later, where he was shot dead.

• 1881, James Garfield (20th president) – Was shot while walking at a train station in Washington, DC, six months after taking office. He died of his wounds a few weeks later. Charles Guiteau, his killer, was found guilty and executed the following year.
• 1901, William McKinley (25th president) –  Was shot at point-blank range after giving a speech in New York. McKinley was expected to make a recovery, but gangrene set around the bullet wounds and he died eight days later. A 28-year-old man from Detroit, Leon F Czolgosz, admitted to the shooting. He was executed a few weeks after the assassination.
• 1912, Theodore Roosevelt (candidate) – Roosevelt was running for the White House as a former president when he was shot in Milwaukee. He survived the shooting but the bullet remained in his chest for the rest of his life.
• 1933, Franklin Roosevelt (32nd president) – Was the target of an assassination attempt in Miami by an Italian immigrant, Giuseppe Zangara. Roosevelt was unharmed, but Anton Cermak, the mayor of Chicago, was killed in the attack.
• 1963, John F Kennedy (35th president) – Kennedy was fatally shot while riding his motorcade through downtown Dallas. He was hit with a high-powered rifle from a distance and died in the hospital a few hours later. Police arrested Lee Harvey Oswald. Two days after the arrest, as Oswald was being taken to jail, he was shot dead by Jack Ruby, a Dallas nightclub owner.

• 1968, Robert F Kennedy (candidate) – The younger brother of John F Kennedy was campaigning for the Democratic nomination and had just won the 1968 California primary election. Right after he gave his victory speech, he was shot dead by Sirhan Sirhan. The killer was arrested and was sentenced to death. That was commuted to life in prison, and his petition for release, in 2023, was denied.
• 1972, George Wallace (candidate) – Wallace was seeking the Democratic presidential nomination when he was shot during a campaign stop in Maryland. He was shot four times and one of the bullets was lodged into his spinal column. That left him paralysed for the rest of his life. The man who shot him was Arthur Bremer. He was convicted and sentenced to prison. He was released in 2007.
• 1975, Gerald Ford (38th president) – Escaped two assassination attempts within 17 days, both in California (in Sacramento and San Francisco) and both carried out by women: Lynette Fromme and Sarah Jane Moore. They received life sentences.

• 1981, Ronald Reagan (40th president) – Reagan was leaving a speech in Washington, DC when he was shot by John Hinckley Jr. The bullet pierced Reagan’s left lung, narrowly missing his heart. Reagan survived the attempt on his life. Hinckley was arrested and found not guilty by reason of insanity. He was confined to a mental hospital.
• 1994, Bill Clinton (42nd president) – Clinton was inside the White House when Francisco Martin Duran fired at the building using a semiautomatic rifle. Clinton was unharmed. Duran was convicted of attempting to assassinate the president and sentenced to 40 years in prison.
• 2005, George W Bush (43rd president) – Bush was attending a rally in Tbilisi with Georgian President Mikhail Saakashvili when a man named Vladimir Arutyunian threw a hand grenade towards the podium. It did not explode and no one was hurt. Arutyunian was sentenced to life in prison.