The Kennedys have always had a lot of friends from the world of Hollywood/Entertainment. (perhaps most famously Frank Sinatra, who supposedly helped JFK win the election by rustling up votes via his, ahem, "connections." Well, and Marilyn, but...that's different. I'm talking about Hollywood types in a chummy way.) JFK and RFK were particularly fond of Judy, and even did what they could (sadly, with little results) to help her as her health spiraled. I remember reading somewhere that they even went so far ask her to move in with them, when she was really down-and-out, they were all so fond of her.
Keep in mind that also, Pat Kennedy (one of JFK and RFK's sisters) was married to Peter Lawford, who made several films with Judy, and they were longtime good friends. (I believe the first film they made together was "Girl Crazy" in 1943, although perhaps their most memorable joint performance was "Easter Parade" (1948), also starring Fred Astaire (trivia: the role was meant to go to Gene Kelly -- who also made several films with Judy, and they were good friends, as well -- but Gene injured himself as filming was supposed to begin, and had to pull out.) Ann Miller also turned in a good performance in the film. The score is by Irving Berlin.
*Ironic note and Gene & Judy: Gene's first picture (previously, his experience had been on the stage, before he was signed by MGM, Judy's home studio.) was "For Me and My Gal" (1942). He often spoke about how nervous he was, and he wouldn't have made it through without Judy. Judy's last completed film for Metro was "Summer Stock" (1950). She was going through a particularly bad patch at the time, and L.B. Mayer asked Gene do do the picture (even though he didn't want to) as a special favor, to help Judy get through it. Which he did splendidly, although Judy was fired shortly thereafter, just as filming of "Annie Get Your Gun" began. (She was replaced with Betty Hutton.) She only made four more films between 1961 and 1963 (and had her own television variety show and a concert or two), before her death in 1969.
Anyway, right up to the end, the Kennedys supported her, when few others did.