I think this started with Teddy, and it infected the whole clan. thereafter, even Bobby, Jr. for a long time .... until recently. The Kennedy Red Pill has taken hold for Bobby, Jr. and the Blue Pill Kennedys need to destroy him.
Now there's just one.
The Progressives.
By the time Papa Joe got around to spawning Ted most of his gene coding related to intelligence had petered out. Literally.