Was Governor George Wallace ever the most powerful politician in America? I have my doubts, but he probably was the most powerful Southern governor during his time as far as the amount of power he had in his state. The Kennedy Administration at least in the early 1960s didn't know how to deal with him because President Kennedy believed he needed the South and even Alabama to get reelected in 1964. But also wanted to pass civil rights laws that Governor Wallace was obviously against.
But the Johnson Administration knew how to deal with him which was by enforcing the Federal court orders and even doing it in public and making the Governor look weak by comparison. And of course that famous Lyndon Johnson treatment where he brings the Governor into the Oval Office and has Wallace saying that "if he stayed any longer LBJ would've had him coming out in favor of civil rights". Governor Wallace was a threat, but how powerful he was is at best an open question. Because the Federal Government whipped in every court battle.