Johnson had dirt on everyone in Washington. Certainly the sexual escapades of John and Bobby were known inside Washington. LBJ could very easily have told the Kennedy’s if they didn’t make him VP, he’d leak solid evidence of JFK’s infidelities to the press.
The Kennedys were no saints either when it came to wielding political power against their enemies and helping out their friends. Jack was probably center of the road in his political leanings for the time, an FDR Democrat. Both Bobby and Ted were left of center.
A retired military officer I knew, who worked in the Kennedy White House, told me Bobby was the most power hungry and ruthless person in Washington, even worse than LBJ. He feared Bobby ever becoming president.
That’s true also, the Kennedy brothers were certainly no saints. LBJ probably did have the goods on a lot of people, I don’t remember if he was good buddies with J Edgar Hoover or not, that would make a difference. Hoover was no saint either and did have a dossier on everybody that walked into the white house. JFK’s womanizing made Bill Clinton look like a choirboy. That’s the common assesment, LBJ threatened to make that public, everyone in the white house was shocked by the announcement he would be JFK’s running mate, only the public was not aware that the two hated each other. LBJ was the last person anyone would have ever guessed JFK would pick.
Your friend may have been right about Bobby, I’m not really sure, don’t know much about that aspect of his career. He and John pissed a lot of people off because they kept them mostly out of the loop, but they still managed to do a pretty good job of things. Boy have the Democrats gone downhill since those days...