To listen to the full debate,

President Bush and his Democratic challenger, Senator John Kerry, exchanged sharp words over Iraq and the war on terrorism in the first of three campaign debates late Thursday.

Throughout the candidates' debate, Mr. Bush defended his decision to invade Iraq, saying it was crucial to the United States' security. Sen. Kerry said going to war against Iraq was a "colossal error of judgment" that diverted America's attention away from the hunt for Osama bin Laden and other members of the al-Qaida terrorist network.

Mr. Bush criticized his Democratic Party opponent for changing his position on key issues, including the war in Iraq, and tried to portray him as indecisive. Sen. Kerry, in turn, questioned the president's credibility and said that Mr. Bush had failed to honor his promises to avoid war except as a last resort.

Thursday's 90-minute debate, broadcast on all major U.S. television networks, focused on foreign policy. President Bush and Sen. Kerry will meet again on Oct. 8, to answer voters' questions, and hold their final debate on Oct. 13, on domestic-policy issues.