That leaves Tuesday night's debate four weeks before Election Day as the only joint town hall that the two are scheduled to hold. The event at Belmont University in Nashville, Tenn., is being moderated by NBC's Tom Brokaw and will include questions on both foreign and domestic policy raised by the audience and voters participating through the Internet.
But the candidates are likely to go after each other on character issues, which McCain's team has forcefully re-injected into the campaign since the weekend.
GOP vice presidential nominee 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. In New Mexico on Monday, McCain himself asked, "Who is the real Sen. Obama?"
Obama retorted in North Carolina that McCain was engaging "in the usual political shenanigans and smear tactics" to distract from economic issues, even as his campaign rolled out a video recounting McCain's involvement in the 1980s Keating Five savings and loan scandal in which the Senate Ethics Committee criticized his "poor judgment."
The newest TV ad from the Obama campaign plays up widespread reports that McCain's focus on the Democrat's past associations is an effort to turn the discussion away from the economy. "As Americans lose their jobs, homes and savings, it's time for a president who'll change the economy, not change the subject," says the ad released Tuesday.
The town hall is McCain's signature - one way he built his "Straight Talk" reputation by interacting with voters in the 2000 campaign and then pulled himself out of single digits to win this year's Republican primary. Since he won the nomination, however, the audiences for these events have needed to get tickets and have not been the come-one-come-all events of the primaries.
Obama has used the town hall format sporadically throughout his campaign, but not recently.
Instead the Democratic nominee has carefully protected his lead with a highly scripted campaign style ever since an off-the-cuff line blew up into a false controversy four weeks ago. Ever since, he's been exclusively sticking to rallies and speeches with a TelePrompTer almost always feeding him prepared text to read.
Obama's last town hall was on Sept. 12 - three days after he went on a riff about how McCain is talking about change when he's really just like President Bush and concluded, "You can put lipstick on a pig."
Obama hadn't even mentioned McCain running mate Sarah Palin before using the line, but the McCain campaign argued it was a clear reference to her signature line during her nomination acceptance speech the week before, when she said the only difference between hockey moms like her and a pit bull is lipstick.
No matter Obama's intent, the debate dominated a full day of campaign coverage and distracted from Obama's plans to focus the campaign on criticism of McCain.
Obama went ahead with two more town halls scheduled for the following three days - one the next day in Virginia, where he lashed out at McCain and the media for blowing up his comment, and another two days later in New Hampshire, where a voter drew the spotlight when he rose and demanded to know when Obama would bring more of a fighting spirit against his critics.
Obama isn't the only one trying to minimize the chance for an unscripted moment at this critical stage of the campaign. McCain still holds his signature town hall meetings but has limited his interaction with the media.
McCain's campaign plane is still emblazoned "Straight Talk Express," but the couch installed at the front doesn't carry reporters for freewheeling conversations like in the early days on his primary campaign bus trips. The town hall debate could be McCain's chance to again to come across to voters as feisty, warm, engaging and quick-witted. Those qualities are harder to show in scripted events.
But a town hall debate is not the same as a town hall campaign event - McCain will be sharing the stage with Obama, and his every word will be parsed.
On the Net:
McCain campaign: http://www.johnmccain.com/
Obama campaign: http://www.barackobama.com/index.php