To take advantage of what may be his last chance to shake things up, McCain will have to perform better than he has in the previous debates. According to the polls, he lost both to Democrat Obama, whom many voters saw as the steadier and calmer candidate.
"The distinction could not be clearer: One guy [Obama] is fighting for you, and the other guy is fighting mad," Obama's running mate, Joe Biden, told a crowd yesterday in Warren, Ohio.
McCain gave a debate preview of his own in Blue Bell, Montgomery County, saying of Obama: "Perhaps never before in history have the American people been asked to risk so much based on so little."
Tonight's subject is domestic issues; the host is Bob Schieffer of CBS News; the site is Hofstra University in Hempstead, N.Y.
The format is similar to that of the first debate Sept. 26. The moderator asks a question and gives each candidate two minutes to answer, followed by five minutes of conversation.
This time, the candidates will sit together at a small table rather than stand at separate lecterns. Such proximity is likely to encourage more direct engagement between the two; in the first debate, McCain barely looked at Obama.
With the stock market down 16 percent since the first debate, the focus is sure to be on the economy and the plans laid out by the candidates this week.
What remains uncertain is whether McCain will pursue the character issues about Obama - including the Illinois senator's association with William Ayers, a leader of the violent, radical Weather Underground of the 1960s and 1970s - that the Republican candidate has raised in commercials and speeches but not in the debates.
Last week, after the second debate, Obama said in a television interview that he had been surprised that McCain had not been willing to raise the matter "to my face."
Yesterday, in an interview with KMOX radio in St. Louis, McCain said he had been "astonished" to hear Obama say "that I didn't have the guts" to talk about Ayers.
Added McCain: "I think he probably ensured that it will come up this time."
Valerie Jarrett, one of Obama's closest advisers, said in an interview Monday that McCain had damaged his own credibility through his frequent changes of tone.
"He's indicated that he may go more positive, but he went so negative that it's hard to pull it back without looking like a tactic," she said. "We keep seeing this erratic behavior, his trying to find what will work instead of just speaking to the interests of the American people."
In the debate, Obama is likely to try to develop the idea that McCain has been erratic; the Obama campaign yesterday put out a memo alleging that "McCain's response to the crisis has careened, sometimes changing course within a single day."
McCain, in addition to working the theme that Obama's election would be risky for America, figures to try again to assert his own independence from President Bush, whose approval rating has fallen to 25 percent.
McCain's stump speech now includes this condemnation of the administration: "We cannot spend the next four years as we have spent much of the last eight: waiting for our luck to change."
New surveys yesterday from the Quinnipiac University Polling Institute underlined how grim the political landscape has become for McCain.
Obama has double-digit leads in Michigan, Minnesota and Wisconsin - three blue states for which the GOP once had high hopes - and a nine-point edge in the red state of Colorado.
He also leads by an average of 13 points in Pennsylvania, where McCain campaigned yesterday and returns tomorrow. Using the debate to move the Pennsylvania numbers will be hard; 40 percent of the electorate lives in the baseball-distracted Philadelphia media market.
On Sept. 14, before the financial crisis broke, McCain led Obama in nationwide polls by about two percentage points. Now, it's Obama who is up, by an average of more than seven points.
"Any realistic chance of McCain coming from behind depends on scoring a knockout in debate," said Peter Brown, assistant director of the Quinnipiac poll. "But given that he has been judged by the electorate to have lost both of the previous faceoffs, that would seem to be a very tall order."
The final faceoff between Barack Obama and John McCain starts at
9 p.m. at Hofstra University in Hempstead, N.Y. Most major network and cable-news channels will carry the 90-minute debate, moderated by Bob Schieffer of CBS News.
Pick Polman's Brain
Log on to philly.com tonight and join the live Web chat with Dick Polman. Chat from 9 to 10:30 p.m. during the presidential debate.
Contact senior writer Larry Eichel at 215-854-2415 or email@example.com.
This article includes information from Inquirer wire services.