This one is tough too.
Both FDR and RFK share a general geographic area and policy preferences. RFK may be a bit more socially liberal and antiwar, but a bit less economically leftist. So its not a perfect Hillary-Bernie map.
It also depends on whether the campaign is 1932 FDR (conservative) vs. President FDR (Communist).
Are you trolling when you call FDR a communist? Because no one who has an understanding of what communism is would call a progressive a communist. As far as I'm aware, FDR didn't support a workers revolution or seizing the means of production from the bourgeoisie