Thanks guys! Good info! Freddy, where do you get your state-by-state numbers? I can only find those for more recent elections; would love to get detailed breakdowns going way back (county level would be even better). So your case, which seems pretty persuasive, is that it’s simple, really: to make a topographical analogy, Maine and Vermont were the mountain peaks of GOP support in previous elections, so in the 1930s the swiftly rising tide of support for the Democrats left those peaks as isolated islands. That about right?
Hari, you probably have a good point there about abolitionism. My impression had been that by 1936 FDR had pulled off the amazing feat of pulling black voters into his coalition (and one would expect civil rights-supporting whites to follow suit) while not (yet) losing the Southern white segregationists; but I was only able to find this source which describes FDR as getting only 23% of the black vote in 1932. The article describes the shift as occurring between '32 and '36, but frustratingly no numbers are given until Truman’s 70% in '48 (at which point Maine and Vermont still went Republican, it should be noted).
Simplico, I like too your characterisation of “white rural northern” states being the only ones that wouldn’t fit into that broad New Deal coalition you described. This seems spot on; but wouldn’t Washington, Minnesota, and Wisconsin also fit that bill? Or were Seattle, Minneapolis/St. Paul, and Milwaukee all even then all big enough to scotch that descriptor?