1948: No third-party candidates

[Unconditional Surrender Truman]

It would be a Truman landslide. Keep in mind that, without Wallace and Thurmond, there would have been less of a perception that Dewey was the inevitable victor. David McCullough argues that Dewey's seeming inevitability kept many Democrats at home in the east coast states, so I could see NY, NJ, PA, MD, and DE flipping, in addition to the South going reluctantly for Truman.

Truman (D): 448
Dewey (R): 83