The melting away of the dollar is like global warming: you can't say that any one heat wave proves the trend, and there might be a cold snap next week. Still, over time, evidence builds up. And so, as the greenback approaches two to the pound, old-timers will remember the fall of sterling, under similar conditions of deficits and imperial retreat, a generation back. We have to ask: is the American financial empire on the brink? Let's take stock.

It's clear that Ben Bernanke got buffaloed, early on, by the tripe about his need to "establish credibility with the markets." There never was an inflation threat, apart from an oil-price bubble that popped last summer. Long-term interest rates would have reflected the threat if it existed, but they never did. So the Fed overshot, and raised rates too much. Now long rates are falling; Bernanke faces an inverting yield curve and even bank economists are starting to call his next move. That will be to start cutting rates, after a decent interval, sometime next year.

Once again, all you monetary policy buffs, in unison please:

The grand old Duke of York, he had ten thousand men.
He marched them up to the top of the hill. And marched them down again.

This is not good news for the dollar.

The US economy is going soft faster than the inflation hawks and growth optimists thought. Housing has been in free-fall for months. With the new Congress anxious to display "fiscal responsibility" - cue Robert Rubin who has moved in very fast on Nancy Pelosi - there won't be any help next year from them. If business investment falls off, recession could hit in 2007 or 2008. With that fear in mind, gloomy profit expectations are setting in, and that's not good for the dollar.

The US trade deficit is near all-time records. By itself, this proves nothing: the US supplies reserves to the world system, and it can run any deficit that the world is prepared to finance. But, sooner or later the world may start to get other ideas.

So here's the big question: is the age of the dollar economy lurching toward an end? Are China, Japan, Saudi Arabia and other big holders of T-bonds about to start a rush, or even a stately promenade, toward the exits? Let's hope not, because the world is unprepared to replace the dollar with anything else. The euro is not suited for the job, and a joint dollar-euro system would need better central bankers than either America or Europe has got. An end to the dollar system would therefore be chaotic, inflationary, and very tough on world trade. The best argument for the dollar has always been: it's not in anyone's interest to bring it down.

Could it happen, though? Yes, it could. And it could be connected to that other unfolding disaster. As the "Pax Americana" goes to hell in Iraq - producing a nervous breakdown among the pro-war elites - let's remember that security and finance are linked. Typically, the country that provides global economic security enjoys the use of its financial assets in world trade. And when the security situation changes, that privilege can be revoked. The consequences are unpleasant. Ask the British: after the sterling area folded, it took a generation for the UK to come all the way back.

That is partly why Economists for Peace and Security - a group I chair - opposed the Iraq war from the beginning. As far back as 2002, we understood - as the economically illiterate neo-imperialists did not - that a world system very favourable to America was on the line. And it was not, as they seemed to think, just a matter of military might. We knew that if the war undermined confidence in the power, good faith and common sense of the United States, that could lead toward disastrous changes on the financial front.

Four years in and with no end in sight, that risk may finally be catching up to the almighty dollar.