Both major parties courted general Dwight Eisenhower, the most popular general of World War II. Eisenhower's political views were unknown in 1948. He was, later events would prove, a moderate Republican, but in 1948 he flatly refused the nomination of any political party.
With Eisenhower refusing to run, the contest for the Republican nomination was between New York Governor Thomas E. Dewey, former Minnesota Governor Harold Stassen, General Douglas MacArthur, Ohio Senator Robert Taft and California Governor Earl Warren. Governor Dewey, who had been the Republican nominee in 1944, was regarded as the frontrunner when the primaries began. Dewey was the acknowledged leader of the GOP's powerful eastern establishment; in 1946 he had been re-elected Governor of New York by the largest margin in state history. Dewey's handicap was that many Republicans disliked him; he often struck observers as cold, stiff and condescending. Senator Taft was the leader of the GOP's conservative wing. He opened his campaign in 1947 by attacking the Democratic Party's domestic policy and foreign policy. In foreign policy, Taft was an isolationist who opposed many of the alliances the U.S. government had made with other nations to fight the Cold War with the Soviet Union; he believed that the nation should concentrate on its own problems and avoid "imperial entanglements". On domestic issues, Taft and his fellow conservatives wanted to abolish many of the New Deal social welfare programs that had been created in the 1930s; they regarded these programs as too expensive and harmful to business interests. Taft had two major weaknesses: he was seen as a plodding, dull campaigner, and he was viewed by most party leaders as being too conservative and controversial to win a presidential election. Taft's support was limited to his native Midwestern United States and parts of the Southern United States.
The "surprise" candidate of 1948 was Stassen, the former "boy wonder" of Minnesota politics. Stassen had been elected governor of Minnesota at the age of 31; he resigned as governor in 1943 and served in the United States Navy in World War II. In 1945 he had served on the committee which created the United Nations. Stassen was widely regarded as the most "liberal" of the Republican candidates, yet as the primaries continued he was criticized for being vague on many issues. Stassen stunned Dewey in the Wisconsin and Nebraska primaries, thus making him the frontrunner. He then made the mistake of trying to beat Senator Taft in Taft's home state of Ohio; Taft defeated Stassen on his home turf and Stassen earned the animosity of the party's conservatives. Even so, Stassen was still leading Dewey in the polls for the upcoming Oregon primary. However, Dewey, who realized that a defeat in Oregon would end his chances at the nomination, sent his powerful political organization into the state. Stassen also agreed to debate Dewey in Oregon on national radio - it was the first-ever radio debate between presidential candidates. The sole issue of the debate concerned whether to outlaw the Communist Party in the United States. Stassen, despite his liberal reputation, argued in favor of outlawing the party, while Dewey forcefully argued against it; at one point he famously stated that "you can't shoot an idea with a gun". Most observers rated Dewey as the winner of the debate, and a few days later Dewey defeated Stassen in Oregon. From this point forward, the New York governor had the momentum he needed to win his party's second nomination.
The 1948 Republican National Convention was held in Philadelphia, Pennsylvania. It was the first presidential convention to be shown on television. As the convention opened, Dewey was seen as having a large lead in the delegate count. His major opponents – Taft, Stassen, and Senator Arthur H. Vandenberg of Michigan – met in Taft's hotel suite to plan a "stop-Dewey" movement. However, a key obstacle soon developed when the three men refused to unite behind a single candidate to oppose Dewey. Instead, all three men simply agreed to try to hold their own delegates in the hopes of preventing Dewey from obtaining a majority. This proved to be futile, as Dewey's efficient campaign team gathered up the delegates they needed to win the nomination. After the second round of balloting, Dewey was only 33 votes short of victory. Taft then called Stassen and urged him to withdraw from the race and endorse him as Dewey's main opponent. When Stassen refused, Taft wrote a concession speech and had it read at the start of the third ballot; Dewey was then nominated by acclamation. Dewey then chose popular Governor Earl Warren of California as his running mate. Following the convention, most political experts in the news media rated the GOP ticket as an almost-certain winner over the Democrats.