Complete the following sentence: Attempts assassination and plots on the president of the United States have been numerous, ranging from the early 19th century to the 2010s. Four sitting presidents have been killed: Abraham Lincoln (1865, by John Wilkes Booth), James A. Garfield (1881, by Charles J. Guiteau), William McKinley (
1901, by Leon Czolgosz), and John F. Kennedy (1963, by Lee Harvey Oswald). Additionally, two presidents have been injured in assassination attempts: Theodore Roosevelt (1912 [former president at the time], by John Flammang Schrank) and Ronald Reagan (1981, by John Hinckley Jr.). In all these cases, the attack weapon used was a firearm.<unk> In all these cases, the attack weapon used was a firearm.