As for what Santourum said in the OP, it's easily possible that America has a direct connection to these assassinations and the president does infact the right to authorise an assassination on an american citizen.
Well, they didn't realy glorify Kennedy. I think it was more of a "Don't mention the bad things about a dead man.".
im not sure if your saying he has the right or doesnt have the right to authorise the assassination of an american citizen. regardless the president does not have the authority to authorize the assassination of an American citizen or any foriegn diplomate or foriegn citizen it is against both US and international law. the president cannot be the judge, jury ,and executioner.
@Frank, yes... dont mention the bay of pigs. xD