Sending troops wasn't possible. FDR had just lost a couple fights with the Congress trying to get us out of the Depression. Remember the attempt to expand the Supreme Court?
But what he did do was to move industry towards a war footing. He also expanded and updated our capabilities in the Pacific. More than most at the time he realized that it would be a two front war and that the key would be industry. That is something you don't just turn on. And had it not been for FDR pushing our industry into a war production mode it would have been a decade later before we were ready to go off to war.
At the time you're speaking about, Britian was not being Carpet Bombed. In fact, carpet bombing did not come in until the US and Britain used it against Germany.
this could be an interesting thread but it is not really on topic here.
If you would like to discuss the events leading up to WWII and the key players, I'd enjoy discussing it with you. This is not the right thread though.
Aslan is not a Tame Lion