Bentsen in 1970 was recruited by John Connally to settle a score with Yarborough (the two hated each other).
As was also the case between Yarborough and Connally's mentor, LBJ. These divisions within the Texas Democratic Party were precisely why JFK went to Texas in November 1963...
EDIT: I didn't see Yankee's post. 
Yarborough was, indeed, a national liberal.
But a populist one, too!
I remember reading about his 1964 Senate race and just ridiculing the very notion of George Bush being elected in Texas . “Aw look, Prescott Bush, sent his boy down here and gonna buy him a Senate seat!” (paraphrased)
IIRC, Yarborough ran about 12 points behind LBJ and almost lost. Who do you think LBJ voted for in the GE? To say nothing about John Connally and the Texas Democratic delegation in Congress?
Johnson, Connally, and Yarborough were all on the same ballot in 1964. Connally did the best out of the three, winning reelection as Governor 74-26%. Johnson beat Goldwater 63-36% in the presidential race. Yarborough had the worst performance of the three, winning 56-44% over the elder Bush. Yarborough didn't "almost" lose, as he still won by a comfortable 12.66% margin. As for Johnson, it was stated by Dan Rather during the CBS News Election Night coverage in 1964 that he voted a "straight" Democratic ticket, including for both Connally and Yarborough. But I'm not sure how Connally would have voted. He certainly voted for Johnson, but given what has been said here about his rivalry with Yarborough, he might have gone for Bush over him.
