Barack Obama was sworn in as president of the United States on the "audacity of hope" but four years on, the great orator - fuelled by such bold optimism and grand promises - appears to have been replaced by a very different man, says Andrew Marr.
Who would have thought it?
Who - left or right, Democrat or Republican - would have believed four years ago, after his ecstatic campaign and election, that Barack Obama would be fighting for his political life?
This was a man once compared, only half jokingly, to a political messiah, a saviour, a faith healer - who could bring Americans together again and wash away the raw anger of the Bush years.
Now he is within an inch of losing to Mitt Romney, a wealthy Republican Mormon who many of his own supporters recently despaired of.
We set out for Chicago, Washington and New York with a simple question: what happened to hope?
Was it that the 2008 financial crash and the threat of a second Depression just blew away the optimism?
Was it his own impossible promises, combined with inexperience? Was it endemic failure in the US political system? Or raw Republican enmity?
Certainly, we heard the most dramatic possible accounts of the awful economic situation which confronted Obama even before inauguration.
Many thought American capitalism itself was about to collapse.
Austen Goolsbee, the Chicago economics professor who helped steer policy through the first part of the Obama administration, described the bad news - coming in a blur of awful figures - as "just one terrifying thing after another".
He had told Obama after one particularly grim session that it might have been the worst background briefing any president-elect had had since Lincoln's in 1861, when the Union was about to break apart.
Obama had glanced up at him and replied: "Goolsbee, that's not even my worst briefing this week."
With a massive fiscal stimulus, Obama saved the economy from total collapse, and on the way saved the imperilled automobile industry.
But some economists thought he got it badly wrong, failing to take the chance to change the system itself.
Jeffrey Sachs, sometimes described as the world's most famous economist, told me he thought adding half a trillion dollars on to the deficit without a plan was "rather shocking".
He did not feel Obama's administration was dealing with the fundamental problems of a deeply unequal and under-invested economy, which had exported too many jobs abroad.
"This is not a country in good shape. We have 15% of the population in poverty, we have one in six or one in seven on food stamps, we have about half of our households within at least twice the poverty line or below, meaning that we have a staggering share of America that is financially struggling right now."
Certainly, it is that sense of a struggling middle class that has dogged Obama's campaign and given Romney some of his best lines.
We spoke to plenty of people who, while applauding Obama's attempt to reform healthcare, thought it had deflected him from the economy and stirred up ferocious hostility he could have done without.
Obama's complex health compromise certainly proved a hard sell.
It produced disastrous 2010 mid-term election results for the Democrats - their worst performance since 1948. After that, Washington was gridlocked and Obama's power at home severely curtailed.
Obama had said "Yes, we can" but he failed to translate a brief sense of common purpose into a movement that would carry him through. On foreign policy, the killing of Osama Bin Laden, and the use of drone strikes - controversial abroad - have been wildly popular.
But Obama's early promises to close Guantanamo Bay and bring about a new era of trust between the US and the Muslim world have turned to dust. He over-promised.
He believed in his own importance as a symbol of change. But a symbol of change and an agent of change are two very different things.
It is quite true that in Congress, the Republicans waged a brutal and remorseless campaign to frustrate him. The level of vituperation and abuse Obama took at the hands of insurgent Tea Party activists went far beyond civilised disagreement.
Yet Obama cannot escape responsibility for his own failure to communicate.
His biographer Jodi Kantor, of The New York Times, speculated that he might rely too much on his own intelligence. "He is an extremely solitary man. He's the most introverted president we've seen in the United States for decades."
As an explainer, Bill Clinton has been far more effective over the past few weeks, to the point where Obama calls him "the Secretary of State for Explaining Stuff".
Yet I came away believing the real reason for that shrivelling optimism of 2008 was deeper.
This is a great country which is losing its economic dominance and has not found any kind of consensus about how it might be recovered. Politicians have loaded the country with debt, much of it now owned by China.
Tough choices have been avoided. As Sachs pointed out, a thicket of dense, semi-corrupt relationships between big money and politics has overgrown Washington.
Meanwhile, increasingly, Americans live in their own separate liberal and conservative worlds, listening to different media, barely conversing. Instead of steering the ship, the crew are throwing punches.
It would have required some kind of saviour to turn all that around.
Obama is a clever and likeable man. But he is not the Messiah.