A look into the World War II section of the FAQ, United States subsection, finds only "Would the US have still gone to war with Germany in WW2 if Hitler hadn't declared war on the US post-Pearl Harbor?", a reply by /u/coinsinmyrocket, but it's only one comment and it's from 3 years ago. (So it's archived, so no new comments can be put there.)
He noted the continuing US+UK talks deciding on a Germany First policy ("Collapse in the Atlantic would be fatal; Collapse in the Far East would be serious but not fatal." - General Marshall), and how the US was pretty much in a shooting war in the Atlantic already, and was giving a lot of military aid to the UK.
But I'd like to see more discussion on his point, "If Germany hadn't declared war on the U.S. , it could be argued that the U.S. may have not declared war on Germany as soon as it did, if at all, especially considering the high feelings of isolationism and 'America First' running through the nation prior to Pearl Harbor.". I wonder whether he might be minimizing that possibility. But I don't know what sources of the time said. I dimly recall seeing the book of New York Times front pages, where the issue after Pearl Harbor had a bit of article that seemed to presuppose an anti-German declaration of war -- but that's a dim memory.
EDIT: I have also tried a search.