Republican John McCain hopes to halt Democrat Barack Obama's momentum and gain new life in the White House race on Tuesday when the presidential rivals meet in their second debate.
With less than a month until the Nov 4 election, the face-to-face debate offers McCain one of his last and best chances to recast a presidential race that has been turning toward Obama in the last few weeks.
"McCain has a big opportunity with this debate," said Peter Brown, assistant director of the Quinnipiac University poll. "He has to change the dynamic and make people re-evaluate Obama."
Obama has solidified his national lead and gained an edge in crucial battleground states as the Wall Street crisis has focused the attention of voters on the economy, an area where polls show voters prefer the Illinois senator's leadership.
A Reuters/C-SPAN/Zogby poll released on Tuesday gave Obama a 3-point edge on McCain, an Arizona senator, but other polls have shown an even bigger margin for Obama.
The economic turmoil continued on Monday, when stocks tumbled on Wall Street in a sign the $700 billion government bailout of US financial concerns did not ease public concerns about the economy.
McCain's campaign has unleashed a volley of attacks on Obama in the last few days as his advisers signaled they wanted to turn the debate away from the economy.
McCain and running mate Sarah Palin have tried to turn the campaign focus back to Obama and his associations with figures like former 1960s radical William Ayers and his former minister, the Rev Jeremiah Wright.
That drew a counter-attack from Obama, who raised questions about McCain's relationship with Charles Keating, a central figure in the US savings and loan scandal in the late 1980s and early 1990s that cost taxpayers billions of dollars.
McCain's aggressive tone and Obama's sharp responses have raised expectations for an explosive debate at Belmont University in Nashville, Tennessee. McCain's last opportunities to change the race could be the debate this week and the final one next week in Hempstead, New York.
"McCain has two more chances within his control to change the race, and those are the two debates," said Todd Harris, a Republican consultant and McCain aide during his failed 2000 presidential bid.
"With less than a month to go, every event is crucial and every big event is exponentially more important than the one before it," he said.
Polls judged Obama the winner of the first debate two weeks ago, but Tuesday's debate will be conducted in a more loose format where questions are asked by the audience a favorite setting for McCain and a staple of his campaigns in the party primaries this year and in 2000.
The questions will be asked by members of a group of about 100 undecided Nashville voters identified by the Gallup polling company. The participants will meet with moderator Tom Brokaw of NBC News and he will select the questioners.
The candidates will sit on stools and be free to roam the stage in a less structured environment.
"It should help him because McCain has done literally hundreds if not thousands of these," Harris said. "At the same time, expectations will be higher for him because he's done so many."
The format also creates a more intimate setting that could inhibit harsh exchanges but force McCain to engage Obama more directly. In the first debate last month, McCain rarely even looked at Obama.