You are saying that the 1945 to early 1960s economy was in shambles before JFK saved us?
!945-1948 started to look ok as people started buying cars after the war, but it soon stumbled, which was one of the reasons that congress allowed us to be dragged into Korea.
By 1955 it was clear that we were headed down at a constant rate. Foird and Chrysler were in trouble, and Studebaker/Packard, as well as wyllys were essentially done. Aerojet dropped the Crosley line, and Kaiser also bailed out.
Taxes kill economies, and the 90+% taxes on producers were a huge anchor dragging everyone down.