With the possible exception of Lincoln, I'm fairly sure that none of those were "political" assassinations(or attempts). All we're either insane, racially motivated(redundancy alert!), attempting to achieve fame(or infamy) or a combination of the above. Altho' Booth(IMO) was nuts too, his motives were political.

I'm sure that a case could be made that Malcolm X's assassination was political. While local and federal law enforcement officials stood aside and let it happen, IMO the main motive was the blood-feud within the Nation of Islam organization. You'd need to use a very loose definition to call that power struggle "political".