Johnson's case was on the front burner at the time, many thinking his career was over. Dig a little further and you have many alleged murders attributed to him. JFK's sins were just not keeping his pants on, and all the insiders already knew this, including Jackie. Not a very strong blackmail, especially when he's being told to take the country to war.
So you believe these very powerful forces (FBI, CIA, Pentagon, Justice) that murdered JFK - and framed Oswald and then covered their tracks - didn't have the ability and resources to frame JFK for something? Their only course was to shoot him in broad daylight in the middle of a crowded street and then frame someone for it? Then cover all of this up?
This is what is odd about the conspiracy claims: these forces can do anything but yet are quite limited at the same time.
BTW: LBJ "escalated" US involvement because the North's attacks on the South increased. The South, after Diem's death, was increasingly incapable of defending itself from the North's increased activity. LBJ was faced with the problem of either abandoning the South to the North or trying to prevent that by increasing the US role. The South simply couldn't do it by themselves.
