The U.S. labor movement was never really explicitly socialist, and certainly not the one that existed during the passage of the New Deal, the GI Bill, the Great Society, etc., and they never had liberals "by the balls"
FDR was not by any means a leftist--he openly pushed the New Deal to save capitalism and steal the thunder from radical leftist movements which were gaining steam in America. This is best evidenced by his attempt at austerity right after his first re-election. Civil rights gained steam when it did partially to prevent black radicals from gaining more steam and partially to save face against the Soviet Union, which quite rightly used Jim Crow in their propaganda. While the early American labor movement as a whole was by no means socialist, the influence of the far-left (and the CPUSA's early organizing efforts in the civil rights movement) cannot be understated.
Admittedly little more than acquaintances, but the influence of Marxism on the early Republican Party is undeniable.
Hard to ascribe the Western Front/Pacific War's success to your idea of liberalism, given that our neutrality ended thanks to Japan directly attacking an American territory and Congress was nearly unanimous in voting for war with both Japan and Germany. And I'm sure the majority of Auschwitz survivors could tell you that the soldiers who freed them were from the east. And of course, post-WWII Western Europe was hardly perfect, given that our main partner in the war had several genocides in its own track record.
Didn't help anyone on earth. Plenty of important space projects, but that was merely the culmination of an international dick-measuring contest.