Sitting US Presidents so far assassinated include Abraham Lincoln in 1865, James Garfield in 1881, William McKinley in 1901 and John F Kennedy in 1963. The very first attempt on a US President was in 1835 against Andrew Jackson, but he survived after the assassins' pistols jammed.
Crooks action might have stemmed from mental illness, or some form of polarisation; either affective or ideological polarisation. The former...