By 1943, Guthrie had a "This Machine Kills Fascists" sticker on the front of his guitar. In 1945, he switched to a Gibson Southern Jumbo and put a larger sticker with the same message on that guitar.
Guthrie viewed freedom vs. fascism as the ultimate battle.
As for socialism or communism, that may be another matter (although Guthrie wrote several anti-Hitler songs).
Oakie Boogie--Jack Guthrie & His Oklahomans (1947)