
In his first term as President (which in reality was most of Roosevelt's fourth term), Truman was confronted by some difficult issues. He approved the use of the atomic bomb on two cities in Japan. He met with the other leaders of the Allied powers at Potsdam, and oversaw implementation of the Marshall Plan in Europe. At home he had to contend with the nation's transition from a wartime to a peacetime economy, one that resulted in what became known as the "Strike wave of 1946". He also supported the recognition of the state of Israel. By the spring of 1948, Truman's public approval rating fell to 36%, and almost everyone assumed that Truman had no chance of winning re-election; almost everyone except for Truman himself. Many Democrats, including FDR's son James Roosevelt. tried to draft General Dwight D. Eisenhower, a highly popular figure whose party affiliation were totally unknown. But Eisenhower emphatically refused to accept their overtures.
Things seemed to go from bad to worse for Truman when, at the 1948 Democratic National Convention, Truman tried to unify his disparate party, which included northern liberals and southern segregationists. He supported a vague civil rights plank in the party platform hoping that this would be something everyone could live with. But an uncompromising and powerful speech given by Mayor Hubert Humphrey of Minneapolis convinced the convention to adopt a stronger civil rights plank, which Truman expressed agreement with. In response, all of Alabama's delegates, and a portion of Mississippi's delegates walked out of the convention in protest. Undeterred, Truman delivered an aggressive acceptance speech attacking the 80th Congress, calling the Republican controlled body the "Do Nothing Congress".
Truman doubled down on his party's civil rights plank. Within two weeks of the 1948 convention Truman issued Executive Order 9981, racially integrating the U.S. Armed Services. He also issued Executive Order 9980 integrating federal agencies. Truman took a considerable political risk in his civil rights platform. Many in his party questioned the political wisdom of these movies, fearing that the loss of "Dixiecrats" would split the Democratic Party. This looked likely to happen when South Carolina Governor Strom Thurmond, a segregationist, declared his candidacy for the presidency on a Dixiecrat ticket and led a full-scale revolt of Southern "states' rights" proponents. A further split in the party occurred when former Vice-President Henry Wallace ran on the Progressive Party ticket, hoping to appeal to the party's left wing. Victory in November seemed unlikely with the party split three ways.
Despite Truman's daunting prospects, he was undeterred. Truman embarked on 21,928-mile "whistle stop" campaign in which he regularly addressed audiences from the rear platform of his campaign train called the "Ferdinand Magellan". He drew large crowds and went on the attack, in contrast with his opponent, Republican Thomas Dewey. Dewey elected to play it safe, believing the unsophisticated polling of the day that predicted that he would coast to an easy victory. The three major polling organizations stopped polling well before the November 2 election date, the very time when Truman's support seemed to surge.
On election day, Truman held his midwestern base. Surprisingly, he won most of the Southern states despite the civil rights plank. He eked out narrow victories in a the critical states of Ohio, California, and Illinois. In the end, Truman won 303 electoral votes, Dewey 189, Thurmond only 39. Henry Wallace got none. The defining image of the campaign came after Election Day, when a jubilant Truman held up the front page of the Chicago Tribune which had an erroneous headline proclaiming "Dewey Defeats Truman."
Despite his election day popularity, Truman's second term would not be an easy one. His opponents still controlled Congress and his desk was full of challenging problems. The Soviet Union's atomic bomb project progressed much faster than had been expected and they detonated their first bomb on August 29, 1949. In response, on January 7, 1953, Truman announced the detonation of the first U.S. hydrogen bomb, which was much more powerful than the Soviet Union's atomic weapons. Then there was also the matter of a war in Korea.
On June 25, 1950, the North Korean army invaded South Korea, beginning the Korean War. In the early stages of the war, the North Koreans easily pushed back their southern opponents. Truman called for a naval blockade of Korea, but due to budget cutbacks, the U.S. Navy could not support such a strategy. Truman then called on the United Nations to intervene. A UN resolution authorized troops under the UN flag led by U.S. General Douglas MacArthur. Truman decided he did not need formal authorization from Congress, a decision he would come to regret. When the conflict resulted in a stalemate, critics called the situation "Mr. Truman's War".
By August 1950, U.S. troops in South Korea (the major part of the UN forces) were able to stabilize the situation. Truman fired Secretary of Defense Louis A. Johnson, replacing him with the retired General George Marshall. UN forces led by General Douglas MacArthur led a counterattack, scoring a surprise victory with an amphibious landing at the Battle of Inchon. UN forces marched north, toward the Yalu River boundary with China. But China surprised the UN forces with a large-scale invasion in November. The UN forces were forced back to below the 38th parallel. By early 1951 the war became a fierce stalemate at about the 38th parallel the original border. Truman rejected MacArthur's request to attack the Chinese. When MacArthur promoted his plan to Republican house leader Joseph Martin, Martin leaked it to the press. Truman fear was that an attack on China would lead to further escalation of the war, drawing in the Soviet Union, which was already supplying weapons and providing warplanes (with Korean markings and Soviet aircrew) to the North Koreans.
On April 11, 1951, Truman fired the popular MacArthur. Of the firing, Truman later famously said, "I fired him because he wouldn't respect the authority of the President. I didn't fire him because he was a dumb son of a bitch, although he was, but that's not against the law for generals. If it was, half to three-quarters of them would be in jail."

Following the dismissal of MacArthur, Truman's approval ratings plummeted. He faced calls for his impeachment, led by Republican Senator Robert Taft. MacArthur returned to the United States to a hero's welcome, and addressed a joint session of Congress. Truman and his generals considered the use of nuclear weapons against the Chinese, but ultimately chose not to escalate the war to that level. The war remained a stalemate for two years. Over 30,000 Americans killed, before an armistice ended the fighting in 1953.
Truman was a strong supporter of the North Atlantic Treaty Organization (NATO), which established a peacetime military alliance with Canada and a number of non-communist European nations. The treaty establishing it was widely popular and easily passed the Senate in 1949. Truman appointed General Dwight Eisenhower as commander. NATO's goals were to contain Soviet expansion in Europe. The original members of NATO were the United States, Great Britain, France, Italy, the Netherlands, Belgium, Luxembourg, Norway, Denmark, Portugal, Iceland, and Canada. The alliance resulted in the Soviets establishing a similar alliance, called the Warsaw Pact.
On the advice of General George Marshall, Truman chose not to offer direct military aid to Chiang Kai-shek and his nationalist Chinese forces in the Chinese Civil War against their communist opponents. Marshall believed that supporting Chiang's forces would drain U.S. resources necessary in Europe to deter the Soviets. When the communists took control of the mainland, establishing the People's Republic of China and driving the nationalists to Taiwan, Truman was blamed by his opponents for losing China to the communists. On June 27, 1950, after the outbreak of fighting in Korea, Truman ordered the U.S. Navy's Seventh Fleet into the Taiwan Strait to prevent further conflict between the communist government on the China mainland and the Republic of China on Taiwan.
In August 1948, Whittaker Chambers, a former Soviet spy, and a senior editor at Time magazine, testified before the House Un-American Activities Committee (HUAC). He said an underground communist network had worked inside the U.S. government during the 1930s, of which Chambers had once been a member. He accused Alger Hiss, until recently a senior State Department official, of also being a Soviet spy. Hiss denied the allegations, he was convicted in January 1950 for perjury for denials under oath. Truman's opponents used the incident to spin the notion that Truman was soft on communism. The Soviet Union's success in exploding an atomic weapon in 1949 and the fall of the nationalist Chinese the same year fueled speculation that subversion by Soviet spies was responsible. Many republicans demanded that communists be rooted out from the government. Truman called the Hiss trial a "red herring". Wisconsin Senator Joe McCarthy accused the State Department of harboring communists and rode the controversy to political fame.
In 1948, Truman ordered an addition to the exterior of the White House: a second-floor balcony in the south portico, which came to be known as the Truman Balcony. The addition was unpopular and Truman's enemies accused him of opulence. The Truman family moved into nearby Blair House during the renovations. As the newer West Wing, including the Oval Office, remained open, Truman walked to and from his work across the street each morning and afternoon. On November 1, 1950, Puerto Rican nationalists Griselio Torresola and Oscar Collazo attempted to assassinate Truman at Blair House. On the street outside the residence, Torresola shot and killed a White House policeman, Leslie Coffelt. Before he died, the officer shot and killed Torresola. Collazo was wounded and stopped before he entered the house. He was found guilty of murder and sentenced to death in 1952. Truman commuted his sentence to life in prison.
Truman also faced more problems on the labor front. In April of 1952, Truman instructed his Secretary of Commerce, Charles W. Sawyer, to take control of a number of the nation's steel mills. Truman justified his action based on the need to maintain an uninterrupted supply of steel for munitions for the war in Korea. The Supreme Court found Truman's actions unconstitutional, however, and reversed the order in its decision in Youngstown Sheet & Tube Co. v. Sawyer.
In his second term, Truman's administration became tainted with scandal. In 1950, a Senate committee, led by Tennessee Democrat Estes Kefauver, investigated numerous charges of corruption among senior administration officials. A number of employees of the Internal Revenue Bureau were accused of accepting bribes. 166 employees either resigned or were fired and many were charged criminally. In 1952 Attorney General J. Howard McGrath fired the special prosecutor for being too zealous. In response, Truman fired McGrath. Corruption became a major issue in the 1952 presidential election.[231][232]
In 1951, the United States ratified the 22nd Amendment, making a president ineligible for election to a third term or for election to a second full term after serving more than two remaining years of a term of a previously elected president. The latter clause would have applied to Truman's situation in 1952, but a grandfather clause excluded the amendment from applying to him. Truman considered running for another term in 1952, and left his name on the ballot in the New Hampshire primary. But the writing was on the wall. This time it was clear that there would be no 1948 miracle. All his close advisers recommended that he not seek another term, noting his age (68) and his poor showing in the polls. Truman had hoped to recruit Dwight Eisenhower as a Democratic candidate, but Ike was more interested in seeking the Republican nomination. When Truman let his name be entered in the New Hampshire primary, he was handily defeated by Senator Kefauver. 18 days later Truman announced he would not seek a second full term.

Truman's unpopularity was an issue in the 1952 election in which Eisenhower, who had gained the Republican nomination, campaigned against what he denounced as Truman's failures. Ike used the alliterative slogan "Korea, communism and corruption". He pledged to clean up the "mess in Washington," and promised to "go to Korea." Eisenhower won the election, ending 20 years of Democratic presidents.