There's no doubt that after June 1941, Roosevelt's administration favored the Soviets over the Nazis.
And doubtless most of that was strictly, "the enemy of my enemy is my friend."
But some was naivety, perhaps deliberate naivety, and some was FDR's hubris in thinking he could deal effectively with Stalin.
Realists at the time and ever since have understood that the Allies' choice was to win back Western Europe for freedom ("half a loaf"), at the sacrifice of Eastern Europe to Stalin, OR, turn over ALL of Europe to the Nazis.
FDR, Churchill & the others chose "half a loaf".
Many Roosevelt defenders blame his policies on naiveté. Please. A man elected four times to the U.S. presidency is not naive. “I just have a hunch that Stalin is not that kind of man. Harry [Hopkins] says he’s not . . . and I think that if I give him everything I possibly can and ask nothing from him in return, noblesse oblige, he won’t try to annex anything and will work with me for a world of democracy and peace.”
His love for the Soviet Union dated at least to 1933 when he recognized them in spite of the Ukrainian famine. He knew Duranty was a fraud. Giving them half of Korea led to the death of 50,000 Americans.