Dathi THorfinnsson said:
If the first bomb or two land on Germany, which promptly surrenders
This could have an enormous impact on Japan's surrender. She was looking for terms as early as April; if FDR is still alive (& he might live another week or two), he might say, "Okay, we'll let you keep an Emperor, just stop fighting." (Or Truman might, if FDR dies even a week or two sooner, no longer needing to hang on til the bitter end; IDK which is more likely: FDR dying early gives Truman a few extra days to get briefed-in.)
You've saved thousands of lives. More important, you've kept the Sovs out of Manchuria, & avoided 50yr of Communist North Korea.
Without the Sov invasion of Manchuria, you've also probably allowed Chiang to win the Civil War.
(AIUI, left-behind equipment gave Mao the needed edge.)
There's half a chance FDR or Truman realizes turning French colonies back is a bad idea, & Vietnam doesn't stay a warzone until 1990.
(That effectively butterflies away Oliver Stone's career.
And "Rambo".
Not to mention "Tour of Duty".
Probably "Magnum" as OTL, too.
)