Truman's social program extending the ideas of the New Deal was referred to as the Fair Deal.
The Fair Deal included laws to expand and support Social Security, raise wages, and prevent racial discrimination in the workplace. However, the economy was a concern after World War II and Congress was unwilling to pass Fair Deal laws during his first term. After winning a second term, Congress agreed to parts of the deal but not the whole program.
Answer: The victory of the Republican candidate, Abraham Lincoln, in the election of 1860. The sectionalism of the 1850s led to a split within the Democratic Party.