"What was the problem?"

Problem was FDR wanted to support the British, who had their backs up against the wall in 1940--and still were virtually alone in late 1941, as you know. But their main adversary was Germany.   And there was a strong isolationist streak in the US, aggravated by the "Merchants of Death" conviction about World War I--and the realization that it had not been the "war to end all wars"--as had been suggested. Though Pearl Harbor brought the US in against the Japanese immediately, it did not automatically mean the US could and would declare war on Germany immediately. However, as I noted, Germany solved that problem by declaring war on the US. So FDR could then ask for a declaration of war on Germany-- and support the British to the hilt, and in the open--not possible up to that time. Up to that time it had been Lend-Lease---and other operations, some not maintaining the US' theoretical neutrality--- like the one memorialized by Woody in "The Sinking of the Reuben James."