Scotland the brave, the USA had a substantial role in WW II prior to Pearl Harbor. Lend-lease, the "Good Neighbor Policy," convoys and the like were in operation well before December 1941. FDR had to perform a delicate balancing act, providing assistance to Britain before without seeming to be too anxious to jump into the fray. And he had to be somewhat duplicitous about it too, particularly during the 1940 elections when he had to make sure that he didn't allow his opponents to paint him as the President that would send America's sons to die in another European war.

Eventually, of course, Pearl Harbor came along and helped our country sharpen its focus -- and Hitler helped by over-ruling his advisors and also declaring war on the USA at that point, making it clear that the USA had to fight both Germany and Japan. After that we were fully engaged, with men and materiel. But it's wrong to say that we didn't help Britain before then; if we really hadn't, it's likely Britain would have lost the war before the Japanese helped us make up our minds.