What if, in 1942, President Roosevelt becomes convinced that the Western Allies should liberate the Channel Islands in 1942 (no Operation Torch is to take place) as a trial of American troops, to test equipment and tactics, and ultimately to provide forward bases and as a major step towards a landing in and the liberation of France?
President Roosevelt is assumed to have made his mind up on this in June 1942, when the Germans and Italians recapture Tobruk. He tells Churchill that Congress will obstruct him as much as possible on any American actions in North Africa in the light of current British failures there and that he has no desire to spend political capital in the face of such opposition.
How soon would the British and Americans be able to attempt an invasion/liberation of the Channel Islands and with what chances of success? (If possible, Churchill will try to ensure nothing is to be taken from the 8th Army in North Africa which would have been historically there until March 1943, due to ongoing fighting with Rommel.)