 Of those who have served as the nation's president, four died in office of natural causes (William Henry Harrison, Zachary Taylor, Warren G. Harding, and Franklin D. Roosevelt), four were assassinated (Abraham Lincoln, James A. Garfield, William McKinley and John F. Kennedy), and one resigned (Richard Nixon, facing impeachment).John Tyler was the first vice president to assume the presidency during a presidential term, and set the precedent that a vice president who does so becomes the fully functioning president with his presidency, as opposed to a caretaker president.The Twenty-fifth Amendment to the Constitution put Tyler's precedent into law in 1967.