In the 19th century Maine voted a little earlier than the other states and often voted for the winner, so there was a saying, "As Maine goes, so goes the nation." After the 1936 there was a revised version, "As Maine goes, so goes Vermont." It may have been Jim Farley who said that.
I always heard the the story with Maine is that it was run by a Yankee Republican machine that despised the French Canadians and Irish who dominated the Dem minority. Since the latter groups had high birthrates, they eventually took over the state after WWII.