FDR dies, and is replaced by someone who doesn't give a snot about liberating Europe from the Reich. Maybe the isolationist in the White House will cite conflict with Japan as a reason to focus on "one war at a time," maybe just "it's across the ocean, in another world altogether" plus no guts or gumption for righteous action.
Or, for whatever reason, D-Day fails, is undermined, or is postponed "indefinitely" for vague reasons, and the Soviets roll over Germany and push further "in hot pursuit of the fugitive Nazi regime" and occupy a very, very handsome chunk of France.
Because the Soviets are a tad stretched at this point, De Gaulle wangles some British and American support (some of the latter is private, fwiw!) and the Free France pick-up team holds onto a chunk of France for themselves.
In exchange for their piddling support, the Americans insist on a grand role in safeguarding Free Paris as a "line in the Seine" for Democracy and Freedom, and, yes, you more swarthy folks kindly use the "colored" water-fountain, please.