To the cheers of an electrified crowd, Bill Clinton swaggered on to the stage of a theatre in Pittsburgh on Thursday night, picked up a microphone, and began a freewheeling, 45-minute Q&A discussion of everything from climate change and foreign policy to education, social justice and what he characterised as the Republican presidential candidate Mitt Romney's iffy record on women's rights.
It was another night in his element for Mr Clinton, who is tirelessly pounding the campaign trail in support of his fellow Democrat. With just over a fortnight until polling day, Barack Obama appears to be clinging to a narrow, but decidedly shaky lead (unless you believe Gallup – see overleaf) in a race now focused on roughly half a dozen swing states. As America's most popular – perhaps only popular – living ex-president, Mr Clinton is one of his biggest assets.
All of this made it strange to see him in Pennsylvania. It is not one of the major "battlegrounds" on which the election result will hinge. In fact, the state is only being vaguely contested, by either party. So why, at this crucial moment in the electoral calendar, did the Democrats deploy one of their brightest stars to a relatively unimportant corner of the electoral map?
The answer, as it happens, lay in the crowd he spoke to. And it, in turn, highlights the great unanswered issue that may decide whether President Obama can win a second four years in office. Mr Clinton was in town for the One Young World summit, an annual version of Davos for the under-30s. And the people in his audience belong to the demographic that hold the key to this election.
In 2008, young Americans owned the presidential battle. They tweeted and watched the YouTube clips that propelled Mr Obama into office. They signed up, unequivocally, for Hope and Change. The pollster John Zogby says the under-30s cast 19 per cent of votes that year, up from 17 per cent in 2004. Their turnout rate was 52 per cent, the highest since 18-year-olds got the vote in 1972.
The outcome? While older Americans were more or less evenly divided between the two candidates, the millions of "extra" young voters broke for Obama, by a margin of two to one. They were, in short, the first black President's margin of success.
This year, things are different. The kids who bought into "Yes We Can" have run out of sunny optimism. And who can blame them? The unemployment rate for under-25s is 13 per cent. More than four million people under 30 are out of work. Many have huge debts: the average university student graduates $27,000 in the red, a figure rising by about 5 per cent a year. For all his soaring rhetoric, Mr Obama has only marginally improved their prospects.
A growing number of under-30s fall into a group that Mr Zogby calls "cengas": people who are college educated and not going anywhere. "These kids are increasingly jaded and increasingly libertarian, in that they have no confidence in government to solve their problems," he says. "Obama still has the black vote, he still has the Hispanic vote, and the creative classes. But young voters are the one part of his core constituency still equivocating."
As a result, his support among under-30s is down by about 10 per cent on 2008. The only saving grace, from the President's point of view, is that, for all their frustration, most deserters are yet to migrate to the Romney camp. Instead they are calling themselves "undecided".
"There are currently double digits in that column," Mr Zogby adds. "The libertarians among them may be rejecting Obama, but they are just as bothered by the Republican Party's invasions of privacy on social issues. So as things stand, it's likely they're just not going to vote. To win, Obama needs to change that, and persuade them to turn out. Getting Bill Clinton to speak to an influential group of young people is a good start. But he's got to do more."
Mr Romney also has problems exciting his base. About 10 per cent of white evangelicals are currently failing to back him, according to Mr Zogby. (One-third of them cite his Mormon faith as the reason.) These voters are also unlikely to vote, Mr Zogby believes. In a way, he says, the race now revolves around two candidates who on paper shouldn't win, "even though one of them has to".
A witness to this fact is Jeremy Epstein, a 20-year-old student and first-time voter from New York who on Tuesday was chosen to pose the first question in the second presidential debate. He asked what each candidate would do to "reassure me that I will be able to sufficiently support myself after I graduate". The query sparked waffle from both candidates, but few specifics. Mr Epstein has said he remains undecided.
Among the younger American delegates at One Young World, there seemed similar confusion. Most seemed instinctively to support Mr Obama, but with pragmatism, rather than messianic zeal. And while the summit is no event for a cynic (other speakers included Jamie Oliver and Bob Geldof), even the card-carrying Democrats there confessed that getting their peers excited about Mr Obama is an uphill struggle.
"There's a different level of enthusiasm," was how one of them, Becky Lynch, euphemistically put it. "Last time, it was so new, and so historic that people were just all in for Obama. Lots of those same people are still supportive. But I'm also seeing a lot of guys who are calling themselves libertarian. I think it's a cynicism thing, a refusal to be part of anything organised. And something about government spending really sets them off."
Glen Grayson, a twentysomething trade union organiser who has been canvassing across the Rust Belt, said younger voters who expected Mr Obama to execute overnight change have been sorely disappointed. "We live in a society of instant gratification," he said. "You want to find something, you have your phone instantly there. You don't have to wait to get home to get email. Everything's instant. And I think that plays a lot into the psychological aspect of politics. People want instant change."
Mr Obama had a chance to puncture their apathy in his first campaign debate. But he instead produced a performance so sloppy and moribund that the comedian Bill Maher, who had recently donated $1m to a pro-Obama lobby group, wondered if the President had "spent all my money on weed". His poll numbers didn't fall much afterwards, but Mitt Romney's ticked vigorously upwards, suggesting that he'd wooed a portion of undecideds.
Some of that damage was undone at this week's town hall debate, when a more energetic President landed some important blows against his rival, before a TV audience that was only marginally smaller than the one for the first debate. Snap poll numbers scored it firmly in Mr Obama's favour, though it will not be until the coming days, when more in-depth polls are published, that we can gauge its lasting impact.
In the meantime, tomorrow brings the third and final debate, on foreign policy, an area widely considered to be Mr Obama's strongest suit. If he can escape serious damage during the portion that covers the White House's disputed response to the killing of the US ambassador Christopher Stephens in Libya, it offers a chance to highlight his credentials as a statesman: the man who killed Osama bin Laden and got troops out of Iraq.
Foreign policy is also an area where Mr Obama may strike a natural chord with young voters. While Mr Romney often seems to base his view of the world on the idea of American "exceptionalism", a pitch more likely to appeal to older viewers, the President sees America as a global citizen. That's more in line with that of the twentysomethings who came of age in a connected world.
If all that fails, the Democrats have one other trump card. Mr Obama may no longer be able to inspire, at least not as he did in 2008. And he has still done too little to lay out his agenda for a second term. But the prospect of a Romney White House may be enough to scare equivocating young voters to the ballot box.
The coming days will see America's airwaves flooded with hundreds of millions of dollars' worth of negative adverts. They will come from both sides, of course. But Mr Obama's will be pitched firmly at ambivalent twentysomethings, highlighting Mr Romney's opposition to abortion and gay marriage, and portraying him as a socially conservative elitist. It won't be pretty, but after four difficult years, a man who won office because of hope is likely to seek re-election through fear.