I’ve read that Stalin was shocked and depressed when the invasion came. Communists in the U.S. were still pro-German for a week afterwards until he gave them the new line.
Noah Goldberg well-covers those actions of the U.S. Left in Liberal Fascism, BTW.
Stalin was shocked and depressed. He hid out in his dacha for several days. Molotov, Kaganovich and others went to plead to him to come out of hiding and lead the nation. When they showed up, Stalin thought they were there to arrest him.