On December 8th 1941, President Franklin D. Roosevelt addressed a joint session of Congress and the Nation via radio. This address came to be known as the "Day of Infamy" speech (cf. the excerpt below). The Senate responded with a near-unanimous vote in support of war.
The following day, December 9th, Roosevelt talked to the Nation via radio. Here is a quote: "In my message to the Congress yesterday I said that we "will make it very certain that this form of treachery shall never again endanger us." In order to achieve that certainty, we must begin the great task that is before us by abandoning once and for all the illusion that we can ever again isolate ourselves from the rest of humanity."