American President Franklin D. Roosevelt called the attack on Pearl Harbor "a date which will live in infamy" to emphasize the unprecedented and deliberate nature of the Japanese military strike against the United States. The phrase "infamy" was used to mark the attack as a shameful and unforgettable betrayal that would be remembered with outrage and sorrow by all Americans. Roosevelt wanted to convey the gravity of the event, the outrage it caused, and the urgent need for the U.S. to respond decisively by entering World War II. By calling it a day of infamy, he highlighted that the attack was an unprovoked act of treachery that fundamentally changed the nation's course and demanded a strong response.

Roosevelt's speech aimed to rally the American people, strengthen national resolve, and unify the country for war, as he assured that the United States would ultimately achieve "absolute victory" over the aggressors. The phrase became emblematic of the attack itself and the subsequent American commitment to the war effort.