Two things here. First, do keep in mind that when you look at the voting records of Southern Senators during the New Deal Era, except for issues of race they were about as liberal as their Northern counterparts. The South prior to the mid-late 20th century was very much underdeveloped, meaning that prior to then an ideology that viewed it as anathema to have the federal government engaged in rural electrification simply wouldn't fly except among the Southern elites. Second off, as a more philosophical question, for those who say that the Democratic Party could retain the solid south by remaining socially conservative but fiscally liberal, I'm wondering what positions would fall under being "socially conservative"? Were race to be one of those issues, I'd imagine that'd cause all sorts of problems for the Party in Northern cities, such then we'd end up with cities like Chicago and New York being Republican strongholds. As of 2010, New York was only ~44% white and only 33% non-Hispanic white, Chicago meanwhile by 1990 was 45.5% white and only 37.9% non-Hispanic white. In short, if this is a scenario where the Democratic Party effectively casts itself as a "national white peoples party", unless the demographic development of major urban areas changes drastically, it'll get demolished in municipal elections. Which, while acceptable for the Southern branch of the Party, is more than slightly problematic from the standpoint of the large Democratic machines that have traditionally existed in urban areas, meaning that more likely than not the Democratic Party would get pushed into moderating those positions so that Northern bosses can remain bosses as opposed to seeing their cities become one party Republican governments. I'd imagine this issue would be far more limited if race didn't fall under the rubric of "socially conservative", but then the question is again, in mid-20th century America what exactly qualifies as "socially conservative"