A rivalry soon simmered between those two and it got nasty. Joe fell for one of the Kennedy girls, I think the one that later married that twit-Brit actor. Joe McC. went to Joe K. and asked for her hand.
This created a huge dilemma for the scheming Kennedy: on the one hand, he'd have loved to have the intermarriage of the ambitious Kennedys with the wildly popular McCarthy; on the other, there was a religious problem: while both Joes were Catholic, McCarthy was divorced & remarried, a major no-no in those days that would have portended trouble among Catholics in the event of a run by a Kennedy nationwide.
In the end, Joe K. refused Joe McC. The latter didn't take it well, and eventually RFK was given the gate. Roy Cohn came smugly to the fore and the rest, as they say, is history. This is one of those facinating "what-if" situations.
P.S. -- to show you the incestuousness of Washington, know ye that Dick Morris is Roy Cohn's nephew!
McCarthy was married only once.