I got the answer. The southerners and catholics has already been discussed. Though it is interesting that if you trace the history of the democratic party all the way through the 1960s, it dominated the south. Now the Republican party dominates the south in the same way the democrats used to.
But union support in the golden age of union power, the 1940s to the 1970s(unsurprisingly also the golden age of America), was overwhelmingly pro-democrat. Unions still tend to support the democrats, but that support has waned a great deal, so that now democrats still do better with unions but do not have the historical domination that they used to.