There's also the fact that a US helmed by FDR was probably the least willfully malicious it's ever been (excepting, possibly, the Lincoln administration). FDR was a racist socdem shit, but comparatively moderate beside the extremely racist hyper-capitalist (or aristocratic slaver, before that) shits that were in charge at all other times. Had he survived longer it's even conceivable the Cold War would have been averted or delayed, though it's likely that his successors would have pivoted to imperialist aggression immediately regardless of how much relations between the US and USSR warmed.

People sometimes forget that liberals can be genuine ideologues and not just cynical opportunists.