 Complete the following phrase:  In the United States, within 100 years, four presidentsAbraham Lincoln, James A. Garfield, William McKinley and John F. Kennedydied at the hands of assassins. There have been at least 20 known attempts on U.S. presidents lives. Huey Long, a senator, was assassinated on September 10, 1935. Robert F. Kennedy, a senator and a presidential candidate, was also 