@FreeDuck,
Quibble away, but (no offense) that's all your argument amounts to.
The last successful presidential assassination was Oswald's killing JFK. Even if you buy the Warren Commission was wrong (and I don't) there's a long list of conspiracy nut suspects and only one involves possible ideological motives. Whether it was Fidel, LBJ, the Mafia, the CIA, or a right wing cabal, they're all unfounded theories, and of them all, the right wing cabal is the least likely. JFK was a lot of things but a leftist he was not. Hell, he was, arguably, more right wing than a lot of today's Republicans.
If the JFK of then ran today most conservatives would vote for him.
Were the attempts against Ford and Reagan ideological? In the case of Ford they were clearly incompetent, but politically motivated? Reagan was lucky because his would be assassin was not incompetent, but he certainly wasn't an ideology either.
MLK's assassin was motivated more by base race hatred than politics and the fellow who shot George Wallace was hardly a civil rights activist.
The last American assassination that can be, arguably, linked to ideology was McKinnleys death at the hand of an anarchist.
God forbid Obama is assassinated, the chances are much better that the assassin will be a maniac looking for eternal fame than service to a cause.