McCain: "Nuclear Iran poses existential threat to Israel and we cannot afford a second Holocaust." Readers may recall that while campaigning last year McCain sang "Bomb Iran" to the tune of the The Beach Boys' Barbara Ann.
Another flashpoint as Obama says McCain claimed we can "muddle through" in Afghanistan. McCain hits back that one might have thought Obama would have visited Afghanistan earlier.
2102 BBC North America editor Justin Webb:
Mr McCain has a slightly patronising tone - I don't think Senator Obama understands etc. Could this work for an older man?
2101 McCain: "I know what it's like when as army is defeated." Showing his experience by referring to his Vietnam service. It turns out both candidates are wearing bracelets belonging to US soldiers who died in Iraq.
Jim Lehrer should cut McCain off, and let Obama speak.
2100 McCain is claiming a long record of making the "right" judgment, against the political current as when he opposed Ronald Reagan's early 1980s deployment of US Marines to Lebanon, where more than 200 of them died in a bombing.
2057 BBC North America editor Justin Webb:
Mr Obama hits a good one suggesting that he won't take lectures on saying unwise things from someone who has sung songs about bombing Iran.
2058 Obama says he said if US has top level al-Qaeda lieutenants in its sights in Pakistan it has to be prepared to take them out if Islamabad won't take action.
McCain is surprisingly coherent tonight. Not nearly the shut out I thought it would be.
2055 On Pakistan, McCain says "if you're going to aim a gun at somebody you better be prepared to pull the trigger". Says Obama threatened to attack Pakistan and this was not the right thing to do.
2053 BBC North America editor Justin Webb:
Victories: Mr McCain has only said "my friends" once (I think) and Mr Obama has not ummed and arred as much as he sometimes does.
2053 Obama says commanders in Afghanistan say they don't have enough troops as too many soldiers are in Iraq. The terrorists who attacked US on 9/11 came from Afghanistan so having four times more troops in Iraq is a "strategic mistake", Obama says.
Michael Graham, The Corner:
It seems to me that John McCain is spending quite a bit of time talking about who he is… rather than either giving specifics that show the work he's done; or even better, laying out what specifically he would do in the future to make life better. Both candidates are underwhelming thus far.
2051 BBC North America editor Justin Webb:
On Iraq, Mr Obama makes the case against the war with elegance, but it's an old case against a decision that is gone and finished. Mr McCain equally elegantly suggests that the issue is how to get out now. On that they neither of them sound so convincing. Mr Obama is listing the points on which Mr McCain was wrong. Does this damage him? I suspect not - you can be wrong but of good character. You can be wrong in the past but right on the future. Mr Obama is making a mistake by getting into petty fights about Senate votes: "I voted for this but against that" etc.
2050 Heated exchange as McCain claims US generals believe Obama's plan would spell danger for Iraq. "Not true, not true," interrupts Obama.
They are really going at each other as McCain repeats the Republican allegation Obama voted against funds for US troops. FYI: The Washington Post ruled this claim was "misleading". Its Fact Checker says Obama voted against the bill alluded to because it did not include a timetable to start bringing US troops home from Iraq.
2046 Obama says: "John, you like to pretend like the war started in 2007." Says McCain was wrong on WMD, and that US troops would be greeted as liberators in Iraq. McCain: "Senator Obama doesn't understand difference between a tactic and a strategy."
2044 Obama says cost of Iraq is nearly a trillion dollars, 4,000 lives, 30,000 wounded and al-Qaeda is stonger than at any times since 2001. "We took our eye off the ball," Obama says.
obama just promised tax cut for all, energy affordable college, healthcare, expand NASA, & rebuild roads & bridges? In 1 breath?really?
2043 Obama says the first question on Iraq is whether they should have gone to war, he points out he opposed it six years ago at huge political risk to himself and says US hadn't finished the job in Afghanistan and caught Bin Laden when it went to war with Iraq.
2042 BBC North America editor Justin Webb:
Now Mr Obama is on the attack with the idea that Mr McCain is a Bush clone and must take responsibility for the Bush years. Mr McCain parries successfully with the fact - and it is a fact - that he and the president have not seen eye to eye on some pretty important questions. Stale. Boring.
McCain says Obama waved the white flag on Iraq by opposing the troop surge, which McCain championed at huge political risk. He is trying to show Obama lacks judgment and is not ready to lead America in its hour of peril.
Another clash as Obama refers to Bush's "orgy of spending". He tries to hang McCain's congressional voting record, which he claims has been with Bush 90% of the time, as a political albatross around his opponent's neck and saying it proves he cannot bring change to Washington.
Ben Smith, Politico.com:
One technological difference here: Only the McCain campaign has young supporters delivering photocopied response points to reporters who are universally on laptops and email in the file center. Obama's all digital.
2037 McCain says Obama's healthcare plan would hand US health system to federal government, repeat of his campaign's attack that Obama's health plan would be government mandated, although Obama campaign insist it's market based.
2036 BBC North America editor Justin Webb:
The questioning is limp, pathetic even. How America misses a John Humphrys or a David Dimbleby - someone who stips out this time-consuming nonsense.
McCain boldly pledges a spending freeze on everything except defence. Obama says "you're using a hatchet where you need a scalpel." Obama decries US deficit spending in Iraq, while that country stockpiles oil surplus cash.
2034 BBC North America editor Justin Webb:
McCain is talking now about the money he saved the taxpayer - people went to federal prison he says. Spenders will be scruubbed - eliminated!
GMC Arder, Belfast, Northern Ireland
They're boring already...and we have to put up with one of them for at least the next four years...God...help the "world" And just a pointer, can I apply for President? Because I've got a pen...too!
2033 Obama says he is accused of being "wildly liberal" but that is just him opposing Bush.
2032 McCain says they must end cost over-runs on swollen defence projects and examine all agencies of government and "eliminate" those not cutting the mustard.
2031 BBC North America editor Justin Webb:
This is a huge disappointment - set piece memorised stuff from both candidates. Nothing revealed about either of them: Obama wants college for everyone in the US - gosh again.
2030 Jim Lehrer asks candidates: "What are you going to adjust in your spending plans to accommodate the Wall Street rescue plan?" Obama pledges to free the US from dependency on Middle East oil by investing in clean energy, healthcare, education and infrastructure. Has he answered the question?
Obama going after McCain directly now. Seeming to get into a groove.
2026 McCain: "Classic example of walking the walk and talking the talk." He says he voted against an energy bill "festooned with Christmas ornaments" and breaks for oil firms which he says Obama voted for. Claims Obama voted to hike taxes on those who make as little as $40,000 a year. "Not true," says Obama.
2025 McCain says a lot of people might be interested in Obama's definition of rich. Obama says he will ensure people who make less than $250,000 a year will see no tax increase, he is giving McCain the laser eyes.
John McCain: "I don't mean to go back and forth" -- Dude, it's a debate, that's what you do.
2022 Obama hammers away again saying President McCain equals another four years of Bush. McCain says he wants to cut business tax so firms stay in America.
Mahabala Shetty, San Diego, United States
McCain was trying to run away from the whole idea of facing Obama citing economic crisis as the reason to go to Washington for cover and face the camera as one observer pointed it out. Obama is going to have a easy task to convince the Americans to elect him over McCain.
2020 McCain says Capitol Hill has "got to be cleaned up" "I was called the sheriff" "I'm no Miss Congeniality"
2020 BBC North America editor Justin Webb:
Mr McCain looks highly prepared - the attack on Mr Obama on earmarks had a nice line or two but I am sure I have heard some before.
2019 Obama agrees that earmarks are wrong, says McCain proposes $300bn in tax cuts to the country's wealthiest people in the country, Obama promises tax cuts for 95% of working families.
Craig Lea, Glasgow, UK
Barack Obama's enthusiasm and charisma will be no match for tortoise John Mccain in today's American media culture - the republicans don't stand a chance.
2017 BBC North America editor Justin Webb:
McCain has a fundamental belief in America - gosh. This would be laughed at in any other western nation as a gambit in a serious debate.
2016 McCain says spending in Washington is out of control, trying to separate himself from eight years of Bush. He says he will veto all pork barrel spending. Says Obama asked for $932m of wasteful federal spending.
2015 BBC North America editor Justin Webb:
Mr McCain's line on holding people accountable was sharp - Mr Obama agreed but then got academic and windy.
2014 McCain praises the qualities of the American worker, he says "our best days are still ahead of us". Both candidates are trying to show they feel the pain of cash-strapped Joe Six Pack.
2012 Obama says "for years the reigning economic ideology has been what's good for Wall Street, not what's good for Main Street". Obama revives McCain's much-derided recent statement that the fundamentals of the American economy are sound.
2011 McCain starts by saying he feels bad about Democratic Senator Ted Kennedy being back in hospital, and says he is pleased blues and reds are reaching across the aisles to sort out the financial morass. He says this will be the "end of the beginning" of the crisis if they can cut a deal.
2010 BBC North America editor Justin Webb:
When McCain said "I havent been feeling too good recently" it certainly got my attention - but he meant about the country.
2009 The two rivals are now vying to be the tough new sheriff of Wall Street.
2007 BBC North America editor Justin Webb:
Barack Obama moves quickly onto the attack - the suggestion that Mccain backed the kind of deregulation that led to the crisis.
Can't remember when I've been this excited about a debate. McCain & Obama should be fun.
2006 Obama says we're involved in two wars and worst financial morass since the Depression. He says there needs to be enough safeguards in any Wall Street bailout to protect taxpayers on Main Street. As expected Obama is trying to link McCain early and often to President Bush and tar his opponent as a deregulator.
2004 Ding, ding, round one. Where do you stand on financial recovery plan?
1959 McCain has reportedly hired a top debating coach who advised him he had his worst debates in the Republican primaries while seated - the format for the third presidential debate next month. McCain has also reportedly been advised to avoid overusing the phrase: "My friends."
1957 In the nearest thing to a presidential debate so far, at a Californian megachurch, McCain is widely perceived to have bested Obama with a straight answer to a question linked to abortion, on which the Democrat was said to have waffled.
1955 BBC North America editor Justin Webb:
The best thing about this debate is its open format. I expect McCain to win in the sense of connecting with America. He needs to use humour to leap artfully over the nonsense of the last few days...
1953 If you've been following this from the start, we've just put up live streamed video from the debating hall, and you can find it if you refresh your page.
Shaun, Shanghai, China
I would like to hear some strategy and solid actions to restore some confidence in the US. We need to hear comments on financial responsibility and regulation as well as foreign policy.
1947 A body language expert told me earlier this year McCain blinks too much when nervous. But he can be quick on his feet in debates and engage an audience with folksy humour. Having said that, satirical US news website The Onion said the other day McCain had a "creepy smile". Struck me as a little harsh.
Paul Volpe, The Washington Post:
Expect McCain to draw heavily on his experiences over the last few days in tonight's debate, casting himself as someone willing to put aside partisanship for the good of the country and Obama as nothing more than a partisan warrior.
1946 Analysts are saying Obama must avoid coming across as too much like the law professor he once was. He can exude an almost Zen-like calm, though at times during debates with Hillary Clinton he is said to have appeared testy. Obama's cool manner is an asset but he will hope to avoid seeming passionless.
1942 In the blue corner we will have Barack Obama. In the red corner, John McCain. I'm picturing the Democrat as a debating gentleman pugilist, an elegant southpaw, and McCain as more of a scrappy slugger, hurling polemical haymakers. To pummel the boxing metaphor, neither wants to be shown up as a lightweight.
Joe Akinmusuru, Ann Arbor, Michigan, United States
This debate is crucial. McCain may be temperamental and shoot off an unguarded comment which can be a winner for him or may confirm his recklessness. Obama on the other hand is noted for being 'cool'. This could come out positive as he may appear unruffled and level-headed, a needed recipe for a multitasking president.
These presidential telly debates have helped pick a winner ever since a youthful and composed John F Kennedy saw off an unshaven, sweaty Richard Nixon in 1960. Will a young pretender cause another upset tonight for an older rival?
I compare Obama to Pinnochio Every time he misleads the american public his ears grow. Watch his ears tonight.
1929 The University of Mississippi, where tonight's debate takes place, became the focus of world attention in 1962 when segregationists rioted in a failed attempt to stop a black student attending the institution. Welcoming a black presidential candidate here this evening, times have certainly changed.
It will be interesting to see how John McCain positions his decision to suspend his campaign to help with bail-out negotiations.
1923 So, McCain is going to turn up after all. A no-show would have angered many in this Republican state and could have backfired spectacularly, gifting Obama a 90-minute national TV platform. But will some voters feel like McCain had to be dragged here kicking and screaming, even though he insists he was trying to help save Wall Street from a financial Gotterdammerung?
This is going to be a running commentary on the first US presidential debate between Republican candidate John McCain and his Democratic opponent Barack Obama, including insights from BBC North America editor Justin Webb, as well as a selection of your e-mails and the best of the blogs. You can send your e-mails here