Franklin D. Roosevelt/Harry S. Truman (D): 421 EV, 55% of the PVRobert A. Taft/Thomas E. Dewey (R): 110 EV, 45% of the PVThe best Mr. Republican could have done against incumbent President Roosevelt in the 1944 Presidential Election. Thanks to Taft's isolationist policies, even during the Second World War, Taft is able to swing Michigan into the Republican column, likewise with New Hampshire which swung in favour of the Republicans thanks to Governor Dewey.
Thus, incumbent President Roosevelt wins reelection in 1944, dies on April 12, 1945 and Vice President Harry S. Truman succeeds Roosevelt to become 33rd President of the United States in April 1945. And the rest of American History is the same as in RL.