The United States had, by 1940, already committed to more or less the Navy, Army, and Air Force that won WW II. Many of the carriers, BB's and cruisers had already been Funded & NAMED a year before Pearl Harbor. Watching the Nazi's wipe out the armies of Europe (and the horror stories that would leak out of the occuppied zones) would do nothing to reduce the American zeal to not get caught short. Ditto for a stronger Japan.
Where did Japan get the oil to survive if it didn't go after the East Indies? Unless they backed out of China, the U.S. wasn't going to trade with them, cutting them off from U.S. oil. The Brits were in control of the Middle East & were nominal allies of the USSR; they certainly weren't going to let Aramco ship oil to Japan even if the U.S. Government would allow it.
By 1950, even with less of a crash program (which I'm not sure still wouldn't happen, given the parameters laid out here) Manhatten would have produced results. The U.S. would have a number of weapons (probably a few less than IOTL, figure around 25-35) and would be just starting to ramp up production; given the nature of Europe's masters. The B-36 might not have been produced, but, given the Meteor and the P-80, it is likely that there would be an U.S. jet bomber (probably more like the Canberra than the B-47, which would be a shame, since the -47 is one of the best designs ever) and some sort of B-52 size/capacity design on the board.
BTW: ITTL the Germans would STILL probably not have a working weapon. The Communist "fellow travelers" who provided the pipeline to the NKVD & Stalin had no Fascist counterparts, meaning the Reich would be either still be chasing their tail or have given up on the Bomb.
It would be an interesting challenge for the Reich. They would still have to get air supremacy AND wipe out the RN before they could move on the UK. (Marine Mammal will not be any easier in this world, perhaps even more difficult, given the increase in weapon lethality per platform and the reliance the Heer would have developed on heavy armor after any protracted campaign in the USSR which will greatly complicate the invasion logistical effort.) The U.S. would proably be willing to, at the least, contribute naval, and probably, air elements to keep the Nazi's on the Continent and as far from the U.S. as possible.