Who would want to be Barack Obama in Copenhagen this December? Mr Obama's election last year was the cause of much delight around the world since it signalled that the US was finally ready to talk seriously about global warming.

But Mr Obama, who is the first US president to push strongly for Congress to enact cuts in its carbon emissions, is beginning to suffer from the problem of high expectations – an exact reversal of how George W. Bush was treated.

Unless something miraculous happens on Capitol Hill, Mr Obama is almost certain to undershoot expectations at the climate change summit in Denmark. Some time in the next two weeks, liberal Democrats will introduce a cap and trade bill in the Senate that will unleash the latest bout of in-fighting within their party following its continued divisions over healthcare reform.

Their differences on climate change are as wide as the Grand Canyon. On the progressive side, there are senators such as John Kerry and Barbara Boxer who want the upper chamber to pass a bill modelled on what went through the House of Representatives in June. This committed the US to reducing its carbon output to 17 per cent below 2005 levels by 2020.

The bill was riddled with loopholes including the fact that it gives away 85 per cent of carbon permits for free and will only move to a system of full auctions in 2030. But against America's past record, most notably the Senate's refusal to ratify the Kyoto Protocol in the 1990s, it marked a big leap forward.

The Senate is very unlikely to pass an equivalent bill between now and December. Against the likes of Mr Kerry and Ms Boxer are a growing caucus of centrist Democrats, from states such as Virginia, Nebraska and Michigan, which have either strong coal-based manufacturing or agricultural lobbies to appease.

Most ominously for supporters of the bill was the ascension last week of Blanche Lincoln, the embattled Democratic senator from Arkansas, to head the Senate agricultural committee. Ms Lincoln, who is facing a re-election battle next year, has described the House cap and trade bill as a “complete non-starter”.

Worse from Mr Obama's point of view is the insistence by a group of 10 Democratic senators, mostly from the Midwest, that they would only support a bill if it included a mechanism to impose “green tariffs” on imports from countries that had not embraced domestic carbon-reduction targets. That means China and India.

Such a move would wreck global climate talks before they got under way. Consider this: the US and other western countries are responsible for at least three-quarters of the existing carbon dioxide in the atmosphere. Both India and China will take a growing share of future emissions but at a fraction the per capita output of the US.

The average Indian, for example, emits two tonnes of carbon a year, against 20 tonnes for the average American. Given India's level of development, any move to reduce its level of emissions would lead to a rise in poverty. More than a third of Indians still have no electricity. Having watched the west grow fat on a high-carbon diet, India would now be asked to lose weight.

Mr Obama will make no such demands on India or China in December. But the fact that he is unlikely to be able to persuade the Senate to pass a reasonable cap and trade bill by then will only underscore foreign scepticism over his ability to deliver.

Unlike the Republicans, who are almost unanimous in opposing limits to US emissions, which they depict as a vast tax increase on Americans and a “jobs killer”, Mr Obama's party is a highly diverse outfit. Some Democrats, such as Mr Kerry, believe nothing can be accomplished in Copenhagen and beyond unless America shows credible leadership.

Others believe that a vote for cap and trade would be electoral suicide. The cost to the American consumer of the bill passed in the House is estimated at between 22 and 49 cents a day – the price of a postage stamp. That, according to most Republicans and a large minority of Democrats, is too high a price. That argument is not likely to cut much ice in Beijing or New Delhi.