These include the power to declare war, coin money, raise an army and navy, regulate commerce, establish rules of immigration and naturalization, and establish the federal courts and their jurisdictions.
It was because the Soviet Union became the focus of Germany's plans of attacking during the war. This became a reason for Stalin to get the Britain and U.S. into action in order to attack Italy so then it will surrender. It effectively made the Germany divert their attention towards the western parts.