Had LBJ remained a senator, he'd probably be thought of as one of the most respected and effective leaders in that office, if a ruthless one; as VP and president, he was horribly outclassed and stepped into a role for which his previous experience had not prepared him. It left him with the legacy of being a defeated president unable to face the humiliation of a probable second term candidacy defeat, and as the national leader ultimately responsible for the deaths of thousands of American soldiers pursuing a failed Vietnam policy.
It was much more within his character to have been brought in on the operation after it was a fait acomplii, to use his new power to ensure that the *official version* of the events prevailed. It seems unlikely that professionals planning the JFK removal would have trusted LBJ in advance, other than with tentative triual balloons about conduct if something very unlucky should happen to president Kennedy.
-ar5chy-/-