Final answer:
President Roosevelt referred to December 7, 1941, as the day that would live in infamy. It was the day of the Japanese attack on Pearl Harbor, leading the United States to enter World War II.
Step-by-step explanation:
The day that President Roosevelt referred to as "a date which will live in infamy" was December 7, 1941. On this day, the Japanese attacked the Pearl Harbor naval base in Hawaii, resulting in the United States' entry into World War II. President Roosevelt's speech on December 8, 1941, was a response to this attack and it urged the American people to unite and take action.
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