John Hinckley, Jr. (failure to launch, leftwing nut ball) attempts to kill Pres. Ronald Reagan(R) with a pistol, but fails. Many others injured in attack, including James Brady (the Brady Bill). Hinckley is currently imprisoned in a psychiatric hospital.
Lynette "Squeaky" Fromme (anarchist nutball, a follower of the Devil's 2nd cousin, Charles Manson) brandishes a loaded .45 cal. pistol at Pres. Gerald Ford(R), but no shots were fired. As of today, she is out on parole.
Sara Jane Moore (serial divorcee` & Leftist revolutionary) fires a pistol at Pres. Gerald Ford(R) - just 17 days after Squeaky's failed attempt. A by stander subdued her. She was later paroled in 2007, from a federal prison after serving more than 30 years.
Lee Harvey Oswald (communist sympathizer who defected to the Soviet Union, and later returned to USA) kills Pres. John Kennedy(D) in his motorcade with a sniper shot. Oswald was later suspiciously killed by saloon keeper Jack Ruby during a custody transfer.
Leon Czolgosz (anarchist & anti-theist) kills Pres. William McKinley(R) with 2 shots from a pistol at the Pan-American Exposition. Czolgosz was electrocuted in the electric chair.
Charles Guiteau (Republican,religious nutball & political hack) shoots Pres. James A. Garfield(R) in the back. The Pres. dies 11 weeks later from infection. Guiteau was hanged for his crime.
John Wilkes Booth (Confederate sympathizer & failed actor, who I'm pretty sure never voted Republican) kills Pres. Abraham Lincoln(R) with a shot to the back of the Pres.' head. Booth was shot & killed during his manhunt.
(source)
Oh. And let's not forget the Left's frenzied love of assassination chic.
The overwhelming conclusion is that many Republican Presidents are frequently and violently targeted by Democrats, Communists & Anarchists.
~Not that facts & evidence matter to Leftists...
Update: Uh, oh. Shameless Protesters Advocate Killing the President.