Maybe the economy being better and Roosevelt more trusted with the public purse would have allowed him to still be POTUS when Japan attacked in February 42. Admiral Yamamoto's post-war memories are fascinating there, how they decided to delay a bit the strike as most of the US Navy had moved to this huge naval base in Thule for its inauguration. Roosevelt's white elephant, the Atlantic's Pearl Harbor that ate so much of the USN budget when they needed it to modernize the fleet and train the sailors...
After that, well, we know how it went, right? A half-finished base that saw all its defenders run away to get back to the Pacific just as they arrived, with obsolete ships and a crazy round-the-world trip. Just like in 1905. Cue Yamato and the decisive battle of Samar wrecking what little forces were remaining. Hitler sent his long range forces from UK and captured the base for a much cheaper price than FDR bought Greenland for, as a very sharp reminder that isolationism doesn't work and leaving UK to starve for a lack of destroyers would come to bite the US in the ass.
Offering an armistice - a peace with honour - there and then was the smartest move Berlin could have done, as we know now the US, even at this low point, could have armed again and crush the Axis, but the US... well, they lost most confidence in themselves and didn't see any way out of the war that wouldn't involve nazi bombers levelling New York.
I read recently a book from a Grossbritannien Reichkommissariat historian who suggested that had the US built up its navy instead of gutting its budget for the Greenland purchase and the Thule Naval Station, they could have found some arrangement with UK, getting access or even full lease on some British bases in exchange for destroyers or any ship that had some ASW capability. Might have kept the Brits in the war a bit longer, even though their defeat was inevitable as we all know.