The feisty Republican tried hard to find a lifeline Wednesday night, challenging his Democratic rival at every turn over his truthfulness, associations and record.
By that measure, McCain won the last debate of the 2008 campaign.
But that may not be enough.
McCain still desperately needs to change the trajectory of a race that's tilting significantly toward Obama. Democratic voters outnumber Republicans, the economic crisis has transformed the race in Obama's favor, President Bush is extremely unpopular, most voters think the country is on the wrong track and the Democrat is leading in key-state polling.
There's little McCain can do on his own to change the dynamic. Not that he didn't try. "I am not President Bush," he said.
"You didn't keep your word," McCain reminded Obama on the issue of accepting public financing, something Obama had said he would do if the GOP nominee followed suit.
McCain, seemingly more prepared and definitely more aggressive than in past debates, called Obama's tax plan "class warfare," accused him of failing to stand up to his party's leaders and said the Democrat twisted his record in ads.
With his repeated attacks, the Republican ran the risk of turning off voters. Their negative impressions of him have risen as he questioned Obama's character over the past week. A New York Times/CBS News poll this week found that more voters see McCain as having waged a negative campaign than Obama.
Yet, McCain had little choice but to turn up the heat -- and endure the consequences.
With the election in less than three weeks, the debate season is over and there are no more high-profile opportunities that can guarantee McCain an audience of tens of millions of people. Flush with cash, Obama has bought 30-minute blocks of prime-time advertising six days before the election; McCain may not be able to afford the same.
Over the next 20 days, both candidates will go after the voters who say they could still change their minds.
There are a lot of them -- about one-third of all voters -- but McCain has to win many more than Obama. Not only is he behind in the polls, but the base of all-but-certain Republican voters is smaller than Obama's Democratic foundation.
The Arizona senator's challenge is great.
In the race for 270 Electoral College votes, Obama has comfortable leads in polls in Democratic-held states and is competitive if not ahead in surveys in Republican bastions. A look at the intensity of candidate visits and television advertising shows the contest is basically playing out in states that Bush won four years ago, with Obama slated to visit Missouri, North Carolina and Virginia this weekend. Only two states that Democrat John Kerry won in 2004, Pennsylvania and New Hampshire, are getting serious attention.
The candidates went into the debate season 20 days ago, virtually tied in polls in the race for the White House.
Since then, Wall Street collapsed, the markets plummeted and the government intervened, putting the economy -- and Bush's policies -- at the forefront of voters' minds.
Again and again, McCain looked directly at Obama and let him have it.
--"You have to tell me one time when you have stood up with the leaders of your party on one single major issue."
--"You're running ads right now that say that I oppose federal funding for stem cell research. I don't. You're running ads that misportray completely my position on immigration."
--"You don't tell countries you're going to unilaterally renegotiate agreements with them."
Obama had a ready answer for McCain and brushed aside the negatives.
"I think the American people are less interested in our hurt feelings during the course of the campaign than addressing the issues that matter to them so deeply," the Democrat said.
McCain's eagerness could be seen in his demeanor as he waited to pounce after each Obama statement. Eyes wide, he breathed deeply, moved his eyebrows up and shot sharp glances in Obama's direction. Obama's usually earnest demeanor, meanwhile, was regularly broken by big smiles as McCain attacked.
Over the course of the debates, a confident and collected Obama held his own in what amounted to an audition for the chief executive position.
He displayed a knack for quick response again Wednesday when McCain raised issue with Obama's links to William Ayers, a radical during the Vietnam War era. "The fact that this has become such an important part of your campaign, Sen. McCain, says more about your campaign than it says about me," Obama said.
The debate said a lot about both candidates. McCain did better Wednesday than ever before but, even as he took punches, Obama succeeded in appearing presidential.