Final answer:
Harry Truman's surprise victory over Thomas Dewey in the election of 1948.
Step-by-step explanation:
In the election of 1948, President Harry Truman, a Democrat, won a surprise victory over the Republican candidate Thomas Dewey.
Despite predictions that Dewey would easily defeat Truman, Truman ran a vigorous campaign and gained support by calling Congress back into session and promoting popular measures like increasing the minimum wage.
The Chicago Tribune famously ran the headline 'Dewey Defeats Truman' on the evening of the election, but Truman actually received 49.5 percent of the popular vote and 57 percent of the Electoral College.