Assassination attempts 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 attempted assassinations: Theodore Roosevelt (1912 [former president at the time], by John Flammang Schrank) and Ronald Reagan (1981, by John Hinckley Jr.). In all of these cases, the attack weapon used was a firearm. Although historian James W. Clarke has suggested that most American assassinations were politically motivated actions, carried out by rational men, not all such attacks have been undertaken for political reasons. Some attackers had questionable mental stability, and a few were judged legally insane. Since the vice president has for more than a century been elected from the same political party as the most recent president, the assassination of the president is unlikely to result in major policy changes. This may explain why political groups typically do not make such attacks.