Exchanges between the candidates have grown ever more acerbic with just four weeks to go until Election Day. Tuesday night's debate gives Republican McCain one of his last chances before a nationwide TV audience to halt the Democrat's momentum and convince voters he is capable of addressing the crisis in the credit, housing and stock markets.
The town hall format at Belmont University will allow voters to ask questions while NBC's Tom Brokaw moderates. The candidates' third and last debate will be Oct. 15 at Hofstra University in Hempsted, N.Y.
If Tuesday night's confrontation echoes the most recent campaign exchanges, it could be far more personal and pointed than the two men's Sept. 26 encounter. McCain's running mate, Sarah Palin, has raised Obama's ties to 1960s-era radical William Ayers and to the Democrat's former pastor, the incendiary Rev. Jeremiah Wright. On Monday, McCain accused Obama of lying about the Republican senator's record, and asked, "Who is the real Sen. Obama?"
Obama's campaign rolled out a video recounting McCain's involvement in the 1980s Keating Five savings and loan scandal, while Obama himself accused McCain of engaging in "smear tactics" to distract from economic issues.
Both nominees have condemned character attacks in the past, and some supporters are urging them to cool the rhetoric.
McCain in June told reporters, "Americans are sick and tired of the personal attacks, the impugning of integrity" in campaigns.
Obama told an Iowa crowd in January: "We can't afford the same old partisan food fight. We can't afford a politics that's all about tearing opponents down instead of lifting the country up."
Some Republicans, while defending McCain's recent tactics, feel he needs to engage voters on the issues, not character, to overtake Obama. Scott Reed, who managed Republican Bob Dole's 1996 presidential campaign, said of the economic crisis: "McCain is suffering because Americans typically punish the party in power."
McCain's best bet, Reed said, is to show voters "who has the best solutions."
Obama adviser David Axelrod told reporters the Democratic nominee wants to focus on economic issues but "we're prepared for a very aggressive debate" if it becomes more personal. "We're running for president of the United States," he said. "It's a rough, tough pursuit."
The debate was being held at a time most Americans have a dismal view of the country's direction.
A Gallup Poll released Tuesday showed just 9 percent say they're satisfied with the way things are going, the lowest ever recorded in the 29 years Gallup has asked the question. Asked to name the country's major problem, 69 percent said the economy. Next closest: 11 percent cited the Iraq war.
Associated Press writer Erik Schelzig contributed to this report.