Romney moves to the centre as Biden tries to rescue Obama
WHO woulda thunk that Joe Biden, of all people, would drag a one-time rock star president over the finish line?
Historically, vice-presidential debates have had little impact on the outcome of presidential elections, but there are exceptions -- and 2012 may be one of them.
In 2004, Democratic challenger John Kerry was up eight points in several polls after besting President George W Bush in their first debate.
But then Vice President Dick Cheney drove home Mr Bush's national-security message in his debate with John Edwards and won on points. Mr Bush's polling stabilised and he went on to win.
Mr Biden may have irritated some voters on Thursday night, but he stopped, or at least slowed, Mitt Romney's momentum and re-energised Democrats.
The contrast between Mr Biden's performance and that of his boss in Denver a week earlier couldn't have been starker. Where Mr Obama never missed an opportunity to miss an opportunity, Mr Biden jumped on every one of Paul Ryan's arguments.
Conservative pundit Dick Morris, who wrote in a mid-debate Twitter post "can't believe how weak Ryan is", knows Mitt Romney must hold senior citizens, the only age group that went for John McCain in 2008.
Unfortunately for the Republicans, Mr Biden clarified that Democrats are the protectors of social security and Medicare.
The same dynamic was at play on abortion, which is of critical importance to undecided women voters who had been moving towards Mr Romney in the last week.
Republicans may say this is a tired evergreen for Democrats and that Ronald Reagan, George HW Bush and George W Bush won with anti-abortion views.
Mr Biden's other achievement was to expose some of the hypocrisy at the heart of the Republican argument. He nailed Mr Ryan for seeking stimulus money for his congressional district while railing against the programme, and for assailing a lack of security at US embassies after he voted to reduce funding by $300m.
Mr Romney will continue to gallop towards the centre, where presidential elections are won. It will be up to Mr Obama to use some of Sheriff Joe's ammo to cut him off at the pass. (Bloomberg)
Jonathan Alter is the author of 'The Promise: President Obama, Year One'