What if the UN commander simply stops at cutting off the North Koreans after the Inchon landings and does NOT invade North Korea?
Republicans in 1952: "Truman lost China, then (through Acheson's "defensive perimeter" speech) practically invited North Korea to attack, then after Americans had died in the ensuing war, deprived MacArthur of a chance for victory and settled for the indefensible boundaries that had led to the war in the first place."
What if the war had been avoided altogether? Even that would not necessarily make Truman very popular. Korea was only one of the reasons Truman was unpopular in 1952. (Others were corruption in government--the "mess in Washington" as the GOP called it; the "loss" of China; the issue of communism in government, which was gaining some traction even before Korea because of the Hiss case, the atomic spies, etc.; and the perceived political ineptness of an administration that couldn't get its program through a Democratic Congress) Truman's job approval numbesr were already below 40 percent in the first half of 1950 (the start of the Korean War temporarily gave him a boost because of the "rally around the president in times of emergency" effect). See the chart of Truman's approval ratings at
http://www.gallup.com/poll/116677/p...ings-gallup-historical-statistics-trends.aspx
Of course it is possible that without the tensions created by the Korean War, Eisenhower would decide not to run, and Taft would presumably be a weaker candidate. But I would not rule out even Taft beating Truman in 1952. Apart from specific reasons for Truman's unpopularity, there would just be a general sense that eleven years as president would be too much for peacetime--a lot of people would be against the idea of a third term for Truman, even though the 22nd Amendment specifically allowed it.
I do think that *if* there is no Korean War, and *if* the GOP nominates Taft in 1952, and *if* Truman decides not to run again, Stevenson might well defeat Taft in 1952. But even that is not a certainty--after twenty years of controlling the White House, there will be a lot of wear and tear for the Democrats.
(On the positive side, the Democrats will have prosperity working for them--but maybe not as much as in OTL, since the OTL prosperity of 1952 was in part fueled by the war.)