Allied Leadership doubts on their eventual victory in World War Two

Question Answered on Quora

Did the Allied leadership, especially in England and America, ever actually doubt their eventual victory in World War Two?

I believe that there was a time from May 1940 (Fall of France) to June 1941 (Operation Barbarossa) where there was considerable doubt in Britain in particular as to whether they could hold out against the Reich. 

During this period the US had not formally entered the war and the Soviets were actually supplying Germany with resources. The Italians went on the offense in the Mediterranean and Greece, Japan was having success in the East and morale was low in the UK following the very poor showing of the BEF forces in France and before that Norway. 

British success at the Battle of Britain, the oratory of Churchill and better showings in North Africa, the Mediterranean and Abyssinia went someway to allay this fear. However these were very dark days