Wikipedia gives the impression that his turn to the right happened before the 1930's, though in 1924, it seems he would still have been a progressive.
I seem to have missed that; back to the drawing board
Edit: Walsh was a massive isolationist and Smith wasn't so that can somehow be the cause of the split.
For the record, to my knowledge, Smith wasn't seen as notably conservative on economics until the '30's, and I remember Mechaman making a reference in IRC once to Smith's programs in New York being called "socialistic". Assuming that the Union dominance keeps up until the end of the decade, maybe a litany of Workers' programs could push our favorite North-Eastern wets to the right of the economic spectrum.