What happened in the Iron Range from 1932–36?

[Senator Incitatus]

Lake County went from the only county Hoover won in the state of Minnesota (43%–35%–19%*) to being Roosevelt's best county in 1936 (80%-18%), and the Iron Range more broadly went from Roosevelt's worst to his best region.

*Socialist Norman Thomas

[If my soul was made of stone]

As you mention, Thomas' influence was much of it, as the heavily unionized region had a strong presence for left-wing third parties prior to the New Deal. On the other hand, the strong CPUSA county of Otter Tail would never go Democratic again after 1932, as that organization collapsed between New Deal deradicalization and the Winter War souring the heavily Finnish populace on the radical left.