Final answer:
The four U.S. Presidents assassinated were Abraham Lincoln, James Garfield, William McKinley, and John F. Kennedy. Their deaths had significant impacts on U.S. history, leading to reforms and immediate shifts in presidential power.
Step-by-step explanation:
The four U.S. Presidents who were assassinated while in office are:
- Abraham Lincoln - the 16th President, assassinated on April 15, 1865.
- James Garfield - the 20th President, assassinated on September 19, 1881.
- William McKinley - the 25th President, assassinated on September 14, 1901.
- John F. Kennedy - the 35th President, assassinated on November 22, 1963.
Abraham Lincoln's assassination, the first of a U.S. President, deeply shook the nation amidst the backdrop of the Civil War. James Garfield was shot by a disgruntled office seeker, and his death highlighted the need for civil service reform. The assassination of William McKinley led to Theodore Roosevelt becoming the youngest president, while John F. Kennedy's death resulted in extensive investigations, including the Warren Commission in 1964.