What sources support that (besides Time Man Of The Year 1938)
the US preferred the Axis to the Soviet Union, but strongly supported the UK over Germany.
That’s simply not true. The US began providing Lend-Lease aid to the USSR in 1941 before entering the war.
I mean before the Nazis invaded the USSR. Public opinion was very anti-Soviet before then.
Anti-Soviet, but still more anti-Nazi. Worth remembering that in the UK the populace was far and away supportive of close ties to the Soviets even after the Pact was signed. There was a downturn for the Winter War but then an uptick again. France however did go off the deep end.