In 1960, John F. Kennedy defeated Richard Nixon by the narrowest of margins. Vice President Nixon had substantial evidence that Kennedy’s allies, in particular, Joe Sr.’s connections stole the election through systematic fraud in critical bellwether states, like Illinois and Texas.
Historian Robert Dallek, who wrote the authoritative biographies of JFK and LBJ, concluded the Daley political machine in Chicago “probably stole Illinois from Nixon.” FBI agents found circumstantial evidence suggesting the same thing.
As for Texas, prominent Lyndon Johnson biographer, Robert Caro notes that LBJ had almost certainly meddled in competitive elections before. If anyone was capable of manipulating the returns in Texas (which JFK won by a mere 46,000 votes), it was Johnson.