Primary campaign
New Hampshire: March 9
Dewey declined to enter the campaign actively while the New York legislature remained in session. In New Hampshire, that meant Dewey relied on the state's Governor, Charles M. Dale, and other supporters to deliver the eight-person delegation to his column. His campaign spent only $9,000.
The result was inconclusive. Dewey took six of the state's eight delegates, and the most popular Dewey delegate outpolled the most popular Stassen delegate by 28,000 votes to 21,000.
Wisconsin: April 6
Wisconsin had proven decisive in 1944 by eliminating Wendell Willkie from the campaign after a poor showing; in 1948, it evolved into a contest between native son Douglas MacArthur and neighbor Harold Stassen of Minnesota. Dewey, maintaining his front-runner approach, remained in Albany and nearly declined to enter the primary, submitting his name only halfheartedly at the last minute.
The Stassen campaign benefited from the large Scandinavian population and the support of Senator Joseph McCarthy, while MacArthur, still in Tokyo, was supported by the La Follette family, the Milwaukee Sentinel, and many of Dewey's 1944 campaigners. McCarthy, a Catholic, criticized MacArthur for his remarriage and divorce; the attack was aimed at the state's large Catholic population. Stassen also succeeded by appealing to both young and liberal voters (through internationalist foreign policy) and conservative and ethnic voters (by calling for a national ban on the Communist Party). In an indirect attack on Dewey, he noted that forty percent of the nation's communists resided in New York.
Though he did not initially campaign in the state, Dewey was weakened by Wisconsin; the leading candidates and other enemies, like former Congressman Hamilton Fish III, had the opportunity to attack him while he remained in New York. Dewey briefly entered the fray in the final days, delivering speeches at Kenosha and Appleton College, and issuing a statewide radio broadcast on April 1 to criticize Stassen's proposed ban on communists, famously arguing, "You can't shoot an idea with a gun."
Stassen won a triumph over MacArthur, taking nineteen delegates to the General's eight. Dewey was shut out, though he captured ten delegates in Oklahoma.
Nebraska: April 13
One week after Wisconsin, Stassen again bested Dewey in Nebraska. Dewey had made a much stronger effort there, having left Wisconsin early to deliver a foreign policy speech in Lincoln. The two were joined on the campaign trail in Nebraska by Senator Robert A. Taft, entering his first primary. Given a break in the Senate schedule for Lincoln's birthday, Taft campaigned in Nebraska, as well as Indiana, Illinois, Minnesota, and Colorado in the span of one week.
Taft was unpopular in the state over his opposition to farm subsidies and unable to campaign until Senate business concluded; he likely preferred to bypass the state altogether. His hand was forced, however, by an independent committee which placed the names of all candidates on the ballot and Senator Hugh A. Butler, who offered Taft the support of his political organization and personally planned a three-day campaign trip for him; he reluctantly agreed. The result was disaster for Taft, who finished a distant third (with only twice the vote of the non-candidate Vandenberg) and a boost for Stassen, who won a clean victory over Dewey.
Now with clear momentum, Stassen appeared to be the favorite for the nomination; he led in the Gallup poll for the first time and was the betting favorite to win the crucial Oregon primary, his next showdown with Dewey. Faced with the definite prospect of a third failed presidential campaign, the press began to write Dewey off. "Although he is not a tragic figure," wrote the liberal magazine The Nation, "there is an element of tragedy in his collapse as a leading contender. ... [H]e has pursued such a cautious course and been so clearly motivated by ambition that he stands for nothing and has no real friends."
Dewey thus decided to stake his political career on Oregon and left for the state on April 20, to establish a campaign and barnstorm for votes.
Ohio: May 4
In January, Stassen made a serious violation of political etiquette by challenging a candidate in his home state. Though Taft personally appealed to Stassen to desist for both candidacies' sakes, the Minnesotan pressed forward with a January 25 announcement that he would controversially file in Ohio, angering Taft and his conservative supporters. Stassen reasoned that he must campaign in the state, since he relied entirely on popular support without establishment backing. After losing Nebraska, Taft hurried home, where he would campaign from April 17 until primary day, speaking eight to ten times per day.
Stassen focused his strength by running a slate of only twenty-three delegates out of a possible fifty-three. Only one, a respected former Ohio Supreme Court justice, ran at-large; the other twenty-two ran in carefully selected districts in the urban centers of Akron, Cleveland, Dayton, and Youngstown. Stassen presumed that voters in these districts would oppose Taft for his sponsorship of the anti-union Taft-Hartley Act.
Taft ridiculed Stassen for vagueness on the issues and took a firm stance in response against universal military training. He proudly spoke in favor of Taft-Hartley and also noted his public housing and education aid bills. Taft's public relations advisor L. Richard Guylay utilized a radio campaign based on the principles of Gustave Le Bon, targeting veterans, young voters, and even union members with a direct appeal to emotion.
The primary was a resounding victory for Taft. Out of the twenty-two district races, Stassen won only nine. His sole delegate at-large finished last. Taft was particularly gratified by the support in industrial regions and told Newsweek that he had received a "new lease on life." Stassen had been dealt his first major blow and permanently alienated the conservative wing of the party in the process. Privately, however, Taft acknowledged Ohio as a Pyrrhic victory; the effort strained his health and budget and gave Dewey a major leg up on both exhausted candidates,.
Oregon: May 21
Beginning after his loss in Nebraska, Dewey prepared for a final stand in Oregon; he proclaimed to advisors that his political career was at stake. Oregon was the only remaining state in which he would compete directly with Stassen for delegates elected by the voters. He had established a campaign strategy in the crucial state in July 1947 with Herbert Brownell and local campaign veteran Ralph Moores, but by March, Moores warned Dewey that the campaign was adrift, and that it would be "desperately hard" to regain the advantage over Stassen.
Dewey enlisted support from various lobbyists and groups, including Winthrop Aldrich, the Brooklyn Real Estate Board, the New York American Federation of Labor, Detroit Edison, the Michigan Alumni Association, Detroit Edison, and the Brotherhood of Railroad Trainmen; he was even backed by lobbyists from the Minnesota Rose Society in Stassen's home state. The campaign established several interest group-specific campaigns, including those for sportsmen, teachers, dentists, lawyers, osteopaths, and farmers. Among those constituencies targeted were the state's 12,000 black voters, who received mailings paying tribute to Dewey's efforts for a landmark anti-discrimination law and practice of race-blind hiring in state employment.
Dewey arrived in the state personally on May 1, campaigning throughout the state; within the first week, he met 35,000 voters. By May 12, Dewey forces had spent $71,000 in the state, most raised by Harold Talbott of the Chrysler Corporation. The campaign would ultimately spend around $150,000, triple the state record, on billboards, radio spots, newspaper advertisements, and half-hour broadcasts. The day before the primary, the Dewey campaign ran a telegram to every physician in the state, written by a former Stassen supporter who had soured on the candidate over socialized medicine.
Stassen, exhausted from his campaign in Ohio, found himself on the defensive for the first time and returned to Oregon earlier than he had planned. His opponents now criticized him for being vague on the issues, including Taft-Hartley, universal military training, and reciprocal tariffs.
Radio debate
Main article: Dewey–Stassen debate
In the final week of the campaign, Stassen returned to anti-communism, the issue which had boosted his campaign to the forefront. Stassen attacked Dewey for a "soft, coddling policy" on communism in the United States and challenged him to a direct debate on the issue—the first ever head-to-head radio debate between two presidential candidates. Dewey accepted, and as the challenged party, chose the format, topic, and rules; the debate would be broadcast nationally on 900 stations from a quiet studio at KEX Portland. The single topic: "Shall the Communist Party be outlawed in the United States?" The debate was heard by an estimated 40–80 million listeners throughout the country, one of the largest audiences in history.
During the debate, Stassen read credited his wartime service and world travels for his belief than an international Communist network demanded immediate, punitive response. Dewey responded with an extemporaneous criticism of the Mundt-Nixon Bill as a "grievous error," and pointed to the fact that Canada had banned communism but still hosted an international espionage ring in the Soviet embassy.
In his concluding remarks, Dewey delivered the most famous lines of the night:
"I am unalterably, wholeheartedly, and unswervingly against any scheme to write laws outlawing people because of their religion, political, social, or economic ideas. I am against it because it is a violation of the Constitution of the United States and the Bill of Rights, and clearly so. I am against it because it is immoral and nothing but totalitarianism itself. I am against it because I know from a great many years experience in the enforcement of the law that the proposal wouldn't work, and instead would rapidly advance the cause of Communism in the United States and all over the world. ... Stripped to its naked essentials, this is nothing but the method of Hitler and Stalin. It is thought control, borrowed from the Japanese war leadership. It is an attempt to beat down ideas with a club. It is a surrender of everything we believe in."
Dewey won the primary by just under 10,000 votes; Stassen no longer had a direct path to the nomination and had failed at establishing himself as the clear popular favorite. Though Stassen had entered the primaries as the presumable heir to Wendell Willkie as the leader of liberal Republicans, the debate over communism had flipped his and Dewey's positions. He now entered negotiations with Taft to block Dewey's nomination at the convention.