what election was the biggest watershed in

[freepcrusher]

establishing the democrats as the liberal party?

Here are some candidates
1932 - FDR era, democrats win massive congressional majorities
1958 - Democrats win a majority of non-southern seats for the first time in 20 years

1974 - Democrats get to 2/3 majorities in house and 3/5 in senate. Many of the freshman of this class help shape the democrats for years to come. After this election, Phillip Burton with the help of the freshman class help get rid of old committee chairman

2010 - blue dog caucus cut in half with remaining democrats more liberal.

[freepcrusher]

not to get off topic but the south in the 1930s was dirt poor and economically populist in the sense of Huey Long or Wright Patman. Of course they strongly supported FDR. Because Roosevelt didn't bring up the integration issue and issues like feminism/abortion rights, GLBT rights etc weren't issues at the time, the south found no reason to vote otherwise.