Final answer:
In the 1948 presidential election, Strom Thurmond ran as a Dixiecrat opposed to civil rights reforms, and Henry Wallace ran as a Progressive after being fired by Truman. Despite these challenges, Truman defeated the Republican candidate Thomas Dewey.
Step-by-step explanation:
In the 1948 presidential election, which was a highly contested battle, two notable candidates broke away from the Democratic Party and ran against President Harry Truman. The first was Strom Thurmond of South Carolina, who ran under the banner of the States' Rights Democratic Party, also known as the Dixiecrats. The Dixiecrats were a pro-segregation group that split from the Democrats due to their opposition to the party's moderate stance on civil rights reforms.
Thurmond's campaign was significant in the Deep South, and he was even declared the official Democratic candidate in Louisiana, Mississippi, Alabama, and South Carolina. The other candidate who left the Democratic Party was Henry Wallace, who had served as Secretary of Commerce under Truman before being fired over differences regarding Truman's policies on the Soviet Union. Wallace then ran as the candidate of the Progressive Party, advocating more liberal policies.
While both of these candidates posed challenges to Truman's reelection bid, ultimately, Truman won the election against the Republican candidate, Thomas Dewey, despite predictions of his defeat and even an erroneous early headline from the Chicago Tribune declaring 'Dewey Defeats Truman'.