Dewey picks Ohio Governor John Bricker for Vice President.
Wallace picks Senator Millard Tydings from the border state of Maryland for Vice President.
This assumes the
solid south stays loyal to the Democrats. With no third party candidate, this is a reasonable assumption.
Wallace does not prevail in 1944, in spite of the fact World War II rages on. The country would simply not accept him as President.
Dewey/Bricker 374
Wallace/Tydings 157
The British voters turfed Winston Churchill in 1945 before the end of World War II, so there is no reason to believe that the U.S. voters would not turf Wallace in 1944.
Churchill lost the election in 1945 after the defeat of Germany, but before the surrender of Japan, so World War II was still on.