Russia was an ally, right up until the end of the war. Then, the end of the war changed the world forever. Some, like Seeger still saw Russia as the good guys and US as the bad. Others saw an impending
"Cold War" and felt as though the principles and foundations of the US were both at risk and worth preserving. It isn't a surprise that the conclusion of WWII would change Seeger's opinion of the war after the fact.