I once argued that if a conservative Democrat had been elected in 1932,
https://www.alternatehistory.com/fo...nt-of-the-united-states.440074/#post-16748284 there could have been a mass Farmer-Labor Party to the left of the Democrats. But Thomas would be a poor choice to head such a party, because he would insist that it be explicitly Socialist.
Yeah I think this or something like it is key. FDR really was an impressive leader who took some risks with very controversial policies. A more moderate, cautious Democrat could easily have ended up with a serious challenge from the left. Something else that would help a lot would be to avoid the crushing of the American socialist movement in the first red scare during and immediately after the US entering WWI.
How about this: POD is Champ Clark wins the Democratic nomination in 1912. He had a majority of delegates in OTL but somehow got outfoxed at the convention anyway, so it's not too much of a stretch. The Republican vote is still split between Taft and Roosevelt, so Clark wins and becomes President. He opposed American entry into WWI IOTL, so unsurprisingly he does so ITTL as well and the US never enters the war. To keep things from diverging too much too quickly I'll say the Allies still pull out a victory. Let's also say Clark ends up being a bit more conservative on the domestic front than Wilson, pushing the Democrats in that direction overall.
So then in the 1920s we have a substantially larger socialist movement than OTL because it never got crushed, and a somewhat more conservative Democratic Party. There's a bit of a feedback loop between those two things with much of the energy that would have gone to left Democrats OTL going to socialists ITTL. Rather than peaking in 1912 at 6% of the popular vote in the Presidential election they gradually grow their vote share and elect a steady stream of candidates to ever higher offices. There's still a stock market crash and a great depression roughly on schedule, but the Democrats elect a moderate in 1932 who is as incompetent as FDR was competent. The 1936 election features that incompetent Democrat, a conservative Republican, and Norman Thomas, who just barely manages to win a popular vote plurality and electoral vote majority in the face of an opposition divided between two not very different candidates.