Rumors of ties between the Kennedys and the Mafia go back to John F. Kennedy's father, Joe Kennedy, who reportedly earned much of the family fortune as a bootlegger ( though his biographer has said this is untrue) and had connections to mobsters like Meyer Lansky. When JFK faced Hubert Humphrey in the Democratic primary in 1960, many claimed that the Kennedy clan called on their mob connections to ensure a favorable vote, and similar accusations were made during the presidential election against Richard Nixon, which Kennedy won by a slim margin.
Several theories tie JFK's assassination to the Mafia. Jack Ruby, the man who murdered Lee Harvey Oswald (JFK's accused assassin), had some minor ties to the mob. One story attributes motive to the Mafia through the Bay of Pigs invasion of Cuba. The Mafia reportedly hated that Cuba was in the hands of Fidel Castro, who had thrown them out of their lucrative Cuban casino businesses when he came to power. The invasion was an utter failure attributed by some to Kennedy's refusal to approve air support.
Another theory involves JFK's brother, Robert, whom JFK appointed to the position of attorney general after he was elected president. Once appointed, Robert Kennedy immediately began a Mafia crackdown. Robert also died from an assassin's bullet.
Another rumor plays on suggestions that JFK kept several mistresses and girlfriends, some of whom were known to associate with mobsters. Some evidence, including federal wiretaps, shows that mobster Sam Giancana may have set JFK up with various women and recorded proof of the President's extra-marital affairs. Conspiracy theorists have speculated hit men sent by Giancana murdered Marilyn Monroe, one of JFK's supposed girlfriends. Giancana himself was murdered shortly before he was due to testify on the Mafia/Kennedy connections.
The Kennedy/Mafia connection is built on a lot of rumor, but the Vegas/Mafia connection is more factual. Almost from its start, the American Mafia operated luxurious, illegal casinos through the United States, bribing local police officers to look the other way. When Nevada legalized gambling in 1931, mobsters were not the first to see the opportunity. The famous Strip was already developing, and a few fancy hotels/casinos were already in place by the time the Mafia arrived.
And when mobsters finally did arrive, it wasn't the usual suspects. Instead, many of the early Vegas casinos were financed by Jewish mobsters like Bugsy Siegel and Meyer Lansky. It cost a lot of money to build casinos, and these men offered shady loans to prospective developers. Some of the loans happened out in the open, with the mob-controlled Teamsters union using its pension fund to finance casino and hotel construction projects. This stopped in 1975, when federal officials took notice.
Casinos generate huge profits, so it didn't take much creativity on the part of the wiseguys to figure out a way to get their cut. They skimmed cash from casinos they partly owned or simply extorted payoffs from casino managers. Many mob bosses were "business partners" with casino owners, whether the owners wanted them as partners or not.
Since the 1970s, the government has been very strict about keeping the mob out of the Vegas casinos. Today, it is believed that the major casinos are not influenced by the Mafia; any hint of an organized crime connection is enough for a casino to lose its gambling license.