American Civil War in the 1930's

Is there any plausible way that a civil war could develop in the 1930's between factions led by FDR, J. Edgar Hoover, or Huey Long? (Besides the "coup" which was being plotted against FDR and was revealed by Smedley Butler).

Coup, yes, war, no

If the Republicans had tried a coup they would have been smashed out of hand. No possibility of a civil war.