If for some reason expanded US use of the bomb in the invasion leads to the USSR being able to gather enough information to build their own quicker, that could affect Truman's chances in 1948. Lets say after a bloody invasion with tens of thousands of US dead, Truman rapidly downsizes the US army even more than OTL because the public is tired of war. Then in the fall of 1948, the Soviets successfully test their first bomb. That would likely shock the public enough to keep the late deciders from voting Truman (they're who won it for him OTL)