The doctrine was developed more fully as an executive branch response following the September 11 attacks. The attacks presented a foreign policy challenge, since it was not Afghanistan that had initiated the attacks, and there was no evidence that they had any foreknowledge of them. In an address to the nation on the evening of September 11, Bush stated his resolution of the issue by declaring that, "We will make no distinction between the terrorists who committed these acts and those who harbor them." The President made an even more aggressive restatement of this principle in his September 20, 2001 address to a Joint Session of Congress: