John F. Kennedy was killed by Lee Harvey Oswald, an ardent pro-Castro Communist. The motive was anger over Kennedy’s policies against Communist Cuba. Since Oswald had applied to immigrate there but been refused, he probably was trying to add something reward-worthy to his immigration resume.
Robert Kennedy was killed by Sirhan Sirhan, a Palestinian terrorist, on the first anniversary of the Six Day War. He was angry about Kennedy’s support of Israel on the campaign trail. He was of Christian family, however, and there doesn’t seem to be any evidence that he had converted to Islam or that it was meant as an act of jihad.
Neither assassin had anything to do with American conservatism or right-wing politics.
Neither assassin’s motive had anything to do with a “climate of hatred” in the US.