For the past decade and more, the world has experienced all the benefits that a globalised economy brings, at small and containable cost. China's phenomenal growth has been only one part of the success story; cheap goods from emerging economies kept the lid on Western inflation and interest rates, while strong global growth opened up new markets for investors and exporters.

Stable or falling real prices of oil, food and commodities, coupled with the productivity gains attributable to new technology, helped to keep the profit margins of many Western corporations at record highs, while unemployment finally started to fall, even in Europe's most over-regulated economies. The anti-globalisation movement, vociferous a decade ago, was relegated to the fringes of public debate. Gordon Brown was not alone in asserting that the world of “boom or bust” was gone for ever, although he may have been alone in believing that the credit for this was all his.

The test of leadership comes now. Keeping globalisation healthy in hard times will be an exacting task. Hard times are upon us. The upward pressure on oil, food and commodity prices - which, incidentally, is driving up costs in China even more steeply than in the West - translates into lower growth and higher inflation. Businesses are cutting investment; consumer spending is faltering; jobs are being cut; and unions are clamouring for “inflation-beating” pay deals that will, if conceded, stoke inflation further.

The difficulty for politicians, particularly in the US and Britain, is that voters have got so used to more or less uninterrupted growth and cheap credit that they feel angry and betrayed. The temptation to search for scapegoats, preferably foreign, is proportionately high. Just when the value of open economies and free trade most urgently needs strong political advocates, they are - predictably but perilously - in short supply.

Goldilocks is having a bad-hair day and, instead of reaching for the hair conditioner, her hairdressers are throwing tantrums. President Sarkozy's ridiculous outburst against Peter Mandelson last week explicitly and falsely asserted that the EU's modest Doha Round offer to reduce farm subsidies and tariffs would cut EU farm production, thus condemning African children to starvation. This is naked, populist, protectionism, built on a manifest untruth: only look at New Zealand, where farm production and exports boomed after the total removal of farm subsidies.

With farm prices high worldwide, there could be no better time than now to lower protectionist barriers, thus encouraging farmers in the developing world. Instead, so far with German backing, France is pushing for “community preference” in agriculture and an even larger Common Agricultural Policy budget, on the pretext of insulating Europe's consumers from high world prices.

Mr Sarkozy's ultimate goal may be to sink the Doha Round altogether. That is hardly a surprise. Affection for open markets has never been France's distinguishing characteristic.

Much more worrying is the resurgence of protectionism in America. In the Democratic primary campaign, both Hillary Clinton and Barack Obama treated free trade as a horseman of the Apocalypse, depicting a world in which American parents and children compete for minimum-wage jobs while corporations heartlessly shift the better jobs overseas.

Mr Obama claims, for instance, that “entire cities...have been devastated” by Nafta, the North American Free Trade Agreement signed in 1993, which he blames for destroying a million American jobs, when in fact total employment has risen by 27 million since 1993, when the trade deficit with Mexico, his favourite scapegoat, accounts for a hardly significant 1.7 per cent of the US economy - and when, overall, job losses attributable to trade rather than to higher productivity amount to only about 2 to 3 per cent of American layoffs.

Should he win, it is possible that Mr Obama will stop talking nonsense like this, for the simple reason that the cheaper dollar has helped to make exports the brightest part of the US economy, accounting for 40 per cent of growth. Optimists point out that he has so far kept quiet on China.

Perhaps he has been told that price inflation is six points lower for blue-collar Americans than for wealthier ones, because poorer people buy more Chinese goods. However, nothing could be less certain than his conversion to free trade, because the Democrats are likely to increase their majority in Congress, and protectionism is raging in Democrat ranks - witness the 2008 Farm Bill, a $290 billion (£146 billion) monument to protectionism.

It has even infected senior Democrats on the party's small free-trade wing. This month Senator Joseph Biden - a potential Secretary of State, should Mr Obama beat John McCain - said this to a meeting in Venice of the Council for Italy and America: “I tell my Senate colleagues that they can't expect American growth to be as high as it was in the Clinton years, because there are 1.2 billion more people out there competing for American jobs.” Did he really think, I asked, that stealing American jobs is what gets those people out of bed in the morning? Or that the global jobs market is a zero-sum game? And if he didn't entertain these two absurd notions, then why use rhetoric that is bound to feed the protectionism that really would kill off American jobs, and European jobs, and all our jobs? His answer: “I'm a free-trader. But I deal in facts.” When men like Mr Biden are saying things like that, it is not clear that even a resounding victory for Mr McCain, a resolute and convinced free-trader, would be enough to save the Doha Round from Congressional defeat.

That is why Europeans must stop resisting the Bush Administration's efforts to set a rigorous timetable, this month at World Trade Organisation negotiations in Geneva, for concluding the Doha Round before autumn. Delay now really does court the risk of failure. The immediate effect on trade might not be dire. America would still be the world's fourth-most-open economy, after Hong Kong, Singapore and, surprisingly, Turkey, and well ahead of the EU. However, the damage of a perceived American retreat from globalisation would be great.

Economic nationalism is perilously contagious. Politicians need to confront popular anxieties about free trade by doing a far better job of explaining how much we gain from the global expansion of wealth and markets that it stimulates - and how much we stand to lose from protectionism. It is precisely because Peter Mandelson increasingly performs this task, that Nicolas Sarkozy would happily throw his head to the poor of Africa. Brains are a typically French delicacy.

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