U.S. President George W. Bush and Senator John Kerry are facing each other before an audience of tens of millions of voters in a high-stakes debate centering on terrorism, the Iraq war and its bloody aftermath.
The 90-minute debate on foreign policy is expected to be crucial for Kerry, who is trailing slightly in recent polls and struggling for momentum less than five weeks before the election.
The Democratic candidate faces the challenge of presenting himself as a credible potential commander-in-chief after a torrent of Republican criticism accusing him of continuously vacillating on major policy issues.
Meanwhile, Bush is expected to face questions on leading the nation into war on the still-unproven premise that Iraq had weapons of mass destruction.
He is also expected to confront accusations that he lacked a post-war strategy to deal with the violence and chaos that have left more than 1,000 Americans dead and that the Iraq war has diverted U.S. attention from al-Qaida and other terrorists.