In 1952, the presidential election was the first of the eventual two battles between Republican nominee, General Dwight D. Eisenhower, and Democratic nominee, Illinois Governor Adlai Stevenson, Eisenhower won both, but had to be coaxed into running in the first place in 1952; only doing so after prodding.
What if Eisenhower does not run, what happens? presuming Stevenson is still the Democratic nominee in this scenario at least.