I wouldn’t expect 0bama to know thing one about the politics that built up to World War II. He doesn’t even show the slightest understanding of situations directly in front of him that would only require a minute amount of common sense.
As for Stalin, he was a shrewd player not to be taken lightly. He really played both sides of the fence. He used his knowledge that Hitler needed him not allied to the west to grab up the Baltic states (Estonia et al) all the while considering that he would eventually be at war with Germany.
His moves stalled for time to get his army better prepared and I would say the only mistake he made was that he thought Hitler would not attack him until Britian was off the board. Even then when Germany did attack he traded land for time and the combination of the Russian Winter and the movement of the Siberian troops to the front (once they knew Japan was not going to attack them) sealed the fate on the Eastern front for Germany.
According to Herman Wouk's account, Stalin was taken by surprise by Operation Barbarossa June 1941. And since his opinion was the only one that mattered in the Soviet Union the Red Army was also surprised. That was nearly a fatal mistake for Stalin personally, and was fatal for millions of Russians. So Comrade Stalin was shrewd and ruthless but he slipped up big time there.