It's only happened one time before that a VP killed the President but the charade that followed has lasted nearly a half century. When Johnson killed Kennedy, they used a lowly government agent as the patsy and set him up to look like a lone killer. With Hoover as the one to fake the evidence, they have had to lie too much over the years.
I think the Clintons would be more direct, just a simple heart attack would do nicely even if it was just food poisoning. Bill Clinton seems to like simple scenarios when he kills his "problems" off.
Johnson just took advantage of the Mafia doing it. Then it was covered up to prevent all the plotting by the CIA, Mafia and the Kennedys against Castro from being revealed.
“Ultimate Sacrifice” puts all the confusing threads together better than any source I am familiar with. Johnson was a murderous SOB with out doubt and could well have known what was coming. But Marcello, Traficante and Hoffa were the main movers taking advantage of their role in the Cuban plots for cover.
Kennedy was killed by Lee Harvey Oswald. An angry, violent and bitter communist who was hated Kennedy.
Many people simply do not want to accept this because it seems so wrong that a nobody like Oswald can strike down a President such as Kennedy. Nobodies are not supposed to drive human events that way.
Case Closed by Gerald Posner is probably the most comprehensive study on this.