President George W. Bush on Sunday strongly defended his domestic spying program, saying it's a limited initiative that tracks only incoming calls to the United States. "It's seems logical to me that if we know there's a phone number associated with al-Qaida or an al-Qaida affiliate and they're making phone calls, it makes sense to find out why," Bush said. "They attacked us before, they'll attack us again." Asked how he responds to Americans worried about violations of their privacy, he said, "If somebody from al-Qaida is calling you, we'd like to know why." The president said that he is conscious of people's civil liberties. "This is a limited program designed to prevent attacks on the United States of America and, I repeat, limited," he said. "I think most Americans understand the need to find out what the enemy's thinking."