Photograph: AFP

Good evening. I know this is a radical thing to say, but I'm going to say it anyway: John McCain needs a "game-changer" if he's going to win tonight's final debate and, just conceivably, the election. (And whether he wins or loses, the pundits really need to stop using the word "game-changer" as soon as possible, because it's starting to get seriously annoying.) The question that's been making headlines, of course, is how McCain will attack Barack Obama over Bill Ayers -- he has signalled that he will, and reacted with visible irritation when Obama expressed surprise that he hadn't said it "to my face" the last time around. (Sarah Palin certainly wants him to be aggressive.) And he's said he'll "whip [Obama's] 'you-know-what'". But McCain's dilemma is that Obama's ever-widening poll lead seems to be based partly on voters responding badly to McCain's. Obama's dilemma -- which could create a crucial moment in a performance we can otherwise exepct to be cool and controlled as per usual -- is how he responds so as to dismiss the matter without looking evasive or untruthful.

The official topic of tonight's 90-minute debate at Hofstra University in Hempstead, on Long Island in New York state -- Christopher Walken's alma mater, by the way -- is domestic affairs. McCain needs to use it to differentiate his new economic plan from Obama's, but that won't be enough to beat the odds now: they're completely stacked against him. Could he concoct some big surprise tonight that doesn't rely on attacking Obama's character -- for example by challenging his rival to more debates, pledging to serve only one term, or promising a bipartisan cabinet, as George Stephanpolous speculates? (A big gesture that doesn't involve pure negativity might appeal, especially if McCain is giving any thought to how to go out a dignified loser, if losing's his fate.) All these questions and more will be answered, or at least pondered in the company of beer and potato chips and salsa, during the course of an all-action liveblog, here from approximately 8.50pm eastern time, 1.50am UK time; the debate begins at 9pm/2am. (You can watch the debate live in the UK on BBC News Channel, Freeview 080). Join me! It'll probably be fun, in a way.

The main difference in tonight's format is that the candidates will be seated at a semicircular desk with the moderator, Bob Schieffer of CBS News. That might seem to favour McCain, who looked restless last time, occasionally wandering around the stage -- but it could also make any contemptuous body language towards Obama, such as not looking him in the eye, seem much worse. (And on MSNBC, Keith Olbermann is speculating even now that the arrangement might force camera angles showing the scarred side of McCain's face.) Continuing our tour of great American beers, tonight's beer is Snake Dog India Pale Ale, from Colorado's Flying Dog Brewery; the drinking game will be improvised as we go along, for maximum alcohol consumption. The presence of an elitist London news editor here at Guardian Election Central tonight means there's also a drink called "wine", though as a regular Joe Sixpack I've no idea what that is.

8.25pm (all times eastern): Comments enabled now. Sorry about that.

8.55pm: The hall is full, and hushed, as we wait to discover exactly how Bob Schieffer will tell everyone to turn their mobile phones off... Ah, here he is, delivering a few words in memory of Tim Russert. (Did a CNN anchor just say that McCain called Hillary Clinton today for tips on handling this debate, by the way? How... curious.)

9pm: Schieffer lays out the format: nine 10-minute sections, with 2-minute responses, then a discussion, in which he'll encourage talk between the candidates. Obama and McCain enter and shake hands, rather warmly, it seemed to me, and with an exchange of pleasantries, though not quite on the "can I call you Joe" level. Schieffer asks them about their rival economic plans, McCain first.

McCain begins with his obligatory Reference to Somebody Who is Ill and Needs Our Sympathy, in this case Nancy Reagan. "America is hurting," he says. We need to put a "floor" under the decline in the housing market. He's setting out his mortgage buyup plan.

9.05pm: Obama says it's the worst financial crisis since the Great Depression, and lays out his four-point plan from earlier this week. He seems to be trying to say "middle-class" as frequently as possible. (Will McCain say it once, even, tonight? He didn't do so in either of the previous debates.) McCain: "I would like to mention that senator Obama was out in Ohio and he had an encounter with a plumber [named Joe]... Joe wanted to buy his business, but he saw you were going to make him pay much higher taxes." Straight onto the tax attack, and a strong start for McCain, though he's blinking madly, it has to be said. "Joe, I want to tell you, I will not stand for a tax increase on small business income... " Then, directly to Obama: "What you want to do for Joe the plumber, and millions more like him" is to prevent him realising the American dream. Obama replies that he'll cut taxes for 95% of Americans, including Joe the Plumber.

Ah, I was wondering when McCain would bring up the key phrase from Obama's encounter with Joe the Plumber -- Obama said he believed in "spread[ing] the wealth around". It's "class warfare", McCain says.

9.12pm: Is Joe the Plumber related to Joe Le Taxi?

9.15pm: Schieffer asks a question the candidates have been asked before, and never quite answered: what will you sacrifice from your policy platforms, given the state of the economy? Obama says he'll go through the federal budget "line by line", eliminating programs that don't work, which isn't technically an answer. McCain: Energy independence! Oh yeah. "We have to stop sending $600bn a year to countries that don't like us very much." McCain promises to take a hatchet to the federal budget and then a scalpel, which is an interesting approach to surgery. (The male undecided Ohio voters on CNN's running display seem to love this.)

...Earmarks, and the Illinois planetarium projector! Time for a drink. I'm growing to love that roguish planetarium projector like an old friend. Obama gives his standard response, which is that earmarks are important (and some of them are "screwy") but don't count for much, especially in comparison to the budget deficit of the last eight years.

McCain -- a good soundbite: "Senator Obama, I am not president Bush. If you wanted to run against President Bush, you should have run four years ago." He repeats the "taxes on anyone earning over $42,000" claim, which Obama rejects by pointing out that even Fox News disputes it. "And that doesn't happen very often."

9.22pm: McCain gets tetchy in response to the suggestion that he votes with his party and with George Bush on pretty much everything.

9.25pm: Both of you pledged to take the high road, Schieffer says, and yet neither of you have done so: he mentions Palin's "pallin' around with terrorists" line. "Are each of you tonight willing to sit at this table and say to each others' face what people in your campaigns have said about each other?" Schieffer seems actively to be trying to provoke a fight here. McCain says none of this would have happened if Obama had accepted his town-hall invitation, and now acts very hurt and wounded about Congressman John Lewis's remarks earlier this week, in which he linked McCain and Palin to civil-rights-era racism in the South.

"Senator Obama has spent more money on negative ads than any political campaign in history, and I can prove it." Tough stuff, though it's always a little strange the way he smiles while he's doing it. Now he accuses Obama of not keeping his word on public finances. "You didn't tell the American people the truth."

9.31pm: Obama himself, in what seems like a defence of Lewis, brings up the shouts of "terrorist" and "kill him" that have been heard at Palin rallies. "Read what he said! You gotta read what he said!" McCain splutters, interrupting. But Obama does call Lewis's comparison with the civil rights era "inappropriate." McCain gets very cross indeed when Obama accuses him of negative campaigning. "Let me just say categorically, I'm proud of the people who come to our rallies," he says, and adds something completely confusing about people wearing hats. "A lot of things have been said at your rallies that I'm not happy with," he tells Obama. It's all about John McCain's wounded feelings tonight, it seems.

9.35pm: via Ezra Klein, it's Joe the Plumber, the friendliest plumber in town! I don't think this is the Joe the Plumber, though.

9.36pm: "Mr Ayers," McCain begins. "I don't care about a washed-up terrorist, but... we need to know the full extent of that relationship." And there's your first reference to Bill Ayers, but McCain doesn't wait, or even press the point much; he moves on to saying that the community organisation ACORN is in the process of perpetrating one of the biggest voter frauds in American history. Which even Joe The Plumber would point out is a ridiculously exaggerated claim that nobody else is making.

"Mr Ayers has become the centrepiece of Senator McCain's campaign," Obama says, talking of how he's "roundly condemned" Ayers's "despicable" acts, and how he served on a school board with Ayers but with various Republicans, too, under the auspices of a close friend of Ronald Reagan's. "Mr Ayers is not involved in my campaign, he has never been involved in this campaign, and he will not advise me in the White House. So that's Mr Ayers."

Obama says his only involvement with ACORN was representing them alongside the US Justice Department. "The allegation that Sen McCain has continually made is that some of my associations are problematic" and so Obama mentions his other "associations" with Warren Buffett, various Republican bigwigs, etcetera. McCain seems frozen and grinning.

9.38pm: McCain says Obama and Ayers sent $230,000 to ACORN, and that Obama launched his political career in Ayers's living room. "That's not true," says Obama. (Maybe it was the kitchen?) "Facts are facts," says McCain, hammering onwards, but CNN's undecided voters aren't interested; the meter is flatlining.

9.45pm: Joe again -- only this time it's Joe Biden, in response to a question inviting the candidates to celebrate the brilliance of their running-mates. McCain ends his Palin pitch with a strange little tribute to Todd 'The Snowmobile' Palin, a smile and a snuffle. Then he starts twitching as Obama speaks; he's a roiling cauldron of emotions tonight, though he's performing much more strongly than last time. CNN's Ohio women, by the way, really really don't like Sarah Palin, but Obama declines an invitation from Schieffer to argue that she's not qualified to govern. That'll be for the voters to decide, he says.

9.47pm: Schieffer wants to ask a question, he says, about "climate control." "Climate change!" McCain snaps back, entirely unnecessarily. While Obama answers, McCain wears a fixed smile, which makes him look like the Joker.

"I admire so much Senator Obama's eloquence," McCain says. Ouch. "He said we should 'look at' offshore drilling. 'Look at' -- you get that? We can drill now!" And what's more, you betcha Joe the Plumber will do the drilling, if you ask him nicely and don't steal all his taxes. Obama says America needs a president who will "enforce unfair trade agreements". Did the McCain perma-grin twitch a little at the slip-up? I think it did, I think it did!

9.53pm: John McCain is a very strange chap. I'm sorry, but there it is.

9.57pm: Do you favour controlling health care costs over expanding coverage? Both, says Obama. McCain wants to put health records online (lots of data entry involved, but maybe Joe the Plumber can do that too?) Oh, and he reprises his $5,000 refundable tax credit for everyone, to which Obama soon gives his oft-heard response: the extra income taxation involved in McCain's healthcare plans would eliminate the benefits.

McCain directly addresses "my old buddy Joe the Plumber". This is getting ridiculous. "If you're out there my friend, and you've got employees and you've got kids, if you don't get the healthcare plan that Senator Obama mandates, he's going to fine you." Obama says Joe the Plumber would pay no fine, because his business is a small business. This debate has now become completely dominated by Joe the Plumber. It's going to be funny tomorrow when Joe the Plumber goes on all the cable networks and reveals that he's a die-hard Ron Paul supporter who thinks money should be abolished.

10.06pm: An abortion question: could either of you ever nominate someone to the Supreme Court who disagrees with you on Roe vs Wade? No litmus test, says McCain. No "strict litmus test," says Obama, but he agrees with Roe vs Wade, and "what ultimately I believe is that women" -- in consultation with family and others -- "are in the best position" to decide.

McCain says that as an Illinois state senator, Obama voted to deny treatment to babies born alive in failed abortions. Obama shakes his head, in a sad, Obama way. Big split between CNN's men and women: the women hate this attack from McCain, but the men love it. "Let me respond to this," Obama says. "If it sounds incredible that I would vote to withhold lifesaving treatment from an infant, that's because it's not true." Obama clarifies his position: he voted against a pro-life bill, but the lifesaving treatment was already legally required. "Another example of Senator Obama's eloquence," McCain snaps back.

Look, it's Barack Obama and Joe le Plumber:

10.18pm: Last question, which seems a little early -- on America's terrible standing in international education league tables. Obama wants investment in early childhood education, and an "army of new teachers" with more pay in exchange for higher standards. "Throwing money at the problem isn't the answer," McCain responds.

...And here's an interview with Joe the Plumber, Joe Wurzelbacher, himself:

Q: Do you think your question surprised Obama, caught him off guard at all?
A: Well that was actually my intent. Most people, you ask them "do you believe in the American Dream?" Nine times out of ten they'll sit there and go, "Yeah, of course!" That's where he messed up, because as soon as I asked him that, his answer shows that he doesn't believe in the American Dream. You know, like the question you asked before – he pretty much contradicted himself. "I don't want to punish you but --" Well, you're going to anyways.

10.25pm: CNN's Ohio voters like Obama's education plans more than McCain's.

10.27pm: A discussion of vouchers in the Washington DC school system. Obama doesn't support school vouchers because the data doesn't support the notion that they work. McCain grins at the entirely comical notion of "data". "Because there's not enough vouchers, therefore we shouldn't do it, even though it works? I got it," says McCain and does one of his terrible Big Mocking Laughs. Nobody else is allowed to laugh even if they wanted to, which makes McCain look awkward.

10.28pm: Closing statements. McCain has a "long record" of being "a careful steward of your tax dollars." It's all about "whether you can trust us or not... that's why I ask you not only to examine my record but my proposals for the future of this country... a long line of McCains have served our country in war and in peace."

10.29pm: Obama: "The biggest risk we could take right now is to adopt the same failed policies and the same failed politics that we've seen over the last eight years and somehow expect a different result." What we need is "a spirit of sacrifice."

...Schieffer: "I will leave you tonight with what my mother always said: go vote now, it will leave you big and strong." Obama and McCain stand and shake hands. "Good job, good job!" McCain tells Obama. And thus ends the forty-ninth debate of the election, if you include the primaries.

10.50pm: CNN's Ohio focus group were entirely unimpressed by all the Joe the Plumber nonsense, and reckon Obama won.

10.52pm: More shortly, when we get the instant polls, etcetera. My take: McCain's strongest performance yet, without a doubt, but that's really not saying very much -- he made Obama's coolness and reserve look a little more like passivity, but on the other hand, he didn't focus his Ayers-related attack at all: he just mentioned Ayers a bit, whereas Obama had a sharp but not-too-short response ready that seemed to draw a line under the matter. Close-ups of McCain's face just don't do him any favours, either; anger, disdain and contempt flicker across his face every few seconds.

10.58pm: Joe Wurzelbacher is on CBS. He says he's uncommitted, but he strikes me as more likely a McCain voter, and says McCain impressed him the most tonight.

11.06pm: CNN instant poll of uncommitted voters: 58% gave the debate to Obama, 31% to McCain; 70% found Obama the more likeable; 22% McCain. No game-changer tonight, then... CBS has similar results, 53% to 22%. That's worse for McCain than both the previous debate snap polls, I think. Even Fox News's focus group, run by Frank Luntz, thinks Obama won.

Here's Joe the Plumber on CBS. And here's some very rapidly produced YouTubery of John "Angry" McCain.

Marc Ambinder: "Tonight, we saw a McXplosion. Every single attack that Sen. McCain has ever wanted to make, he took the opportunity tonight to make. Around 30 minutes in, McCain seemed to surrender the debate to his frustrations, making it seem as if he just wanted the free television."

So there you have it. Barack Obama won, John McCain didn't, not least because he simply can't control his annoyance and his contempt for his rival. But the real winner was Joe the Plumber. And also Democracy. Which means that, in a very real sense, it was a victory for America, and for each and every one of us.

And so, goodnight: my regular blog will continue through to the election. Of course, I'll be liveblogging election night, and quite possibly various other pre-election events as circumstances warrant. Thanks for reading and commenting...