Speech by very popular Governor Huey P. Long in 1934. Can you imagine if a Louisiana Governor gave this same speech today? So what caused this shift in Louisiana politics towards the right?
The Longs themselves, as well as the civil rights movement.
Earl Long capitalized on civil rights and had a pretty strong power base among black voters. Plus, Earl managed to maintain Huey's political machine, which was extremely corrupt and nepotistic (mafia involvement, oil scandal, the "deduct" box, etc.).
So politics in Louisiana during the Long era was about Longs and anti-Longs, not necessarily left and right. Civil rights was all tied up with that.