I don't know about the American government, but Churchill foresaw the outcome on the Eastern Front basically from the very beginning of Operation Barbarossa. Even as the German army advanced deep into Soviet territory, he was betting that the Soviet Union's superior manpower, industrial capacity, and resource availability would ultimately lead to victory. This was likely a major reason Churchill later supported a "soft underbelly" strategy - basically invading Italy and the German-occupied Balkans from bases in North Africa - as opposed to invading occupied France via Normandy or the Pas-de-Calais. He believed that by liberating these regions before the Soviets could advance that far, the Western Allies could prevent them from falling into the Soviet sphere.

Obviously, that's not how it actually played out. Although the Allies did invade Italy, that advance stalled around halfway up the peninsula as the focus shifted to the Normandy invasion and advance through France. Allied forces in Italy did eventually break out towards the tail end of the war, but by then the Soviet Union had already occupied a huge swath of central and eastern Europe, as well as the Balkans.

Source: Kissinger, Henry. Diplomacy. New York: Simon & Schuster, 1994