By Justin Webb
A spate of head-scratching is sweeping the usually self-confident United States, as political commentators warn of the decline of the great nation.
These so-called "declinists" are nothing new - they have been issuing their gloomy predictions since Russia beat the US into space - but with rocketing debt and fractious political battles, their argument has more weight than ever.
Is there fear in the eyes of the Mount Rushmore presidents?
When I lived in Washington DC as the BBC's North America editor, we used to drive the children two hours north to Hershey's Chocolate World.
Amid the glorious chocolatey smell, you are greeted by a film that sums up US optimism.
"Milton S Hershey, father of the American chocolate industry, started in failure and ended in success, because he was honest, smart and believed that a good tasting product was more important than anything else," booms the all-American voice.
It reflects perfectly the attitude of mind that built the US - naive in many ways, unworldly in its unquestioning attitude to commercial enterprise, yet wholesome, rugged and, to use Donald Rumsfeld's favourite phrase, forward leaning.
Oh man, life was simple in those days. It was 1886 and the United States was reaching the end of a century it began with its status and future very much in question and ended on course to become the richest, most powerful nation on earth.
As the chocolate museum makes clear, Milton S Hershey was one of many honest, smart, dedicated people who made America great.
Interestingly, the nation built much of that greatness on a foundation of debt. But Americans convinced the world, during the 19th Century, that they would always be able to pay it back.
They prospered, repaid the loans and borrowed more. They invented mass consumer debt too - and used it to power an economy that would change history.
The US is in debt again to the tune of trillions of dollars, a greater proportion of her national wealth than at any time since World War II.
US politicians warn of a "tidal wave of debt" sweeping the nation
But this debt, some say, is not the benign force that previous debts have been. This debt is the potential cause of the decline of the US, which starts with the economy but quickly encompasses everything, taking a whole culture down.
Former State Department official Richard Haass, President of the Council on Foreign Relations, says this single issue has the power to critically damage the US at home and abroad.
If US politicians do not address the country's debt, and find a more sustainable trajectory, he says, Americans will one day wake up to find the world has done the job for them.
"The bond market will essentially lose confidence in the ability of the US to repay its debts and it will force us to raise interest rates dramatically," he says.
"That would obviously have tremendous consequences for economic growth."
That would be serious in itself. But it is the effect on US power and thus on all of us that Richard Haas wants to bring to our attention.
WHAT IS DECLINISM?
Commentators in the United States have often worried that the country's position as the world's most powerful and wealthy nation is under threat.
Every generation has its own fear. In the 1960s, following Soviet successes in space, many in the US felt it was falling behind technologically.
In the 1970s, as Japan experienced an economic boom, declinists warned that the US's place as the economic frontrunner was in jeopardy.
"It will very much contribute to a weakening of the United States, it will diminish our capacity to act in the world and to lead. And I don't see anyone else stepping up to take our place in a responsible way.
"So the 21st Century will turn out to be a century of much greater disorder, of a weaker US."
What is interesting about the declinists' case is that it has little to do with the obvious foreign threats to the power of the United States.
The real problem is an inability to get the nation, as they see it, to wake up to impending disaster and mend its ways.
There is an interestingly moral tone to their argument. The point is that the US debt - her accumulated deficits - cannot easily be addressed without serious and painful changes to society, probably including tax rises and an end to some entitlements.
Barack Obama's budget hinted at what has to be done but in truth would do little to address the fundamental problems that cause the US to function, or fail to function, as it does.
One of the issues the declinists point to is the odd fact that the US political system is so rooted in a constitution signed off in the 18th Century.
Francis Fukuyama, one of the US's great thinkers, points out that the nation's love for guns is not just about personal protection.
"Americans love guns, not because they like to hunt but because they feel, if they're faced with tyrannical authority, if they're armed they've got a way of resisting," he says.
"There's a level of political distrust in the country broadly that makes a kind of reasonable formation of political consensus extremely difficult."
Fukuyama says the political system needs fixing and many in the US would agree.
But while most would say the answer is a move to the centre ground and an agreement by all on what needs to be done, there are some who take the opposite view.
On one hand Tea Party activists are sick of the cosy Washington consensus which they say is corrupt and expensive.
On the other are people like the Economist and Professor at Columbia University Jeffrey Sachs, who believes the problem is actually too much agreement - a system which he says relies so heavily on funding from business that the interests of the wealthy are always super-protected.
"Both parties have adopted a low tax, favour the rich, do very little reform strategy," he says.
"The reality is our politics is guided by money at the top in an age that exceeds the gilded age."
Is there any hope for the US? Well yes, for two reasons.
Will the US flag continue to flutter over the world?
First, the declinists have been around in various guises before and they have always been wrong. The US has an ability to cope with its problems that no other country has ever matched.
Secondly, the US has some key advantages in a world of digital knowledge and technology.
Virtually all the world's great universities are there and, as Anne-Marie Slaughter of Princeton says, one of the first things they teach is to question the teacher.
This, she says, is the US's crucial advantage.
"I don't think we're the only nation that can invent great technologies, I don't think we have a lock on intelligence or education," she says.
"But that cultural characteristic of welcoming, indeed requiring, the challenging of authority - in a world where knowledge, ideas, innovation is the currency - we're very well placed.
"We need to renew our social contract, our infrastructure, our physical infrastructure, our education infrastructure, our health infrastructure.
"There's a great deal of work to do, but we are not losing the capability to do it."
Take that, declinists! The United States' greatest days are ahead