https://en.m.wikipedia.org/wiki/Edward_J._KingThe man himself was a conservative/populist Democrat. I think he could unite the Bob Casey, Joe Biden, and Jimmy Carter types alongside Catholics who voted for Kennedy in 1980. If anyone could unify the 1970s/1980s Lower Southern Democrats, the Catholics, the populists, and the Scoop Jackson neoconservatives, it would be him.
How well would he do in the primaries if he got endorsements from, say, Reubin Askew, Jimmy Carter, Howell Heflin, Philip W. Noel, and J. Joseph Garrahy?