Barack Obama enters his first real moment of global diplomacy in London on Wednesday with a paradox: he is the most popular US president in a generation but you would have to go back more than two generations to find one with fewer cards to play.
Many outside the US accept that the country is not solely to blame for the global meltdown. None would point the finger at Mr Obama personally. But it is he who will be the target of long pent-up resentment at the US's evangelical approach now that its belief in self-regulating markets has been discredited.
Thursday's G20 summit, and Wednesday's meetings between Mr Obama and Dmitry Medvedev and Hu Jintao, his Russian and Chinese counterparts, will focus on the future rather than the past. But it is in shaping the future that Mr Obama is likely to find his greatest difficulties.
Unlike his predecessors who created the Bretton Woods currency system in 1945 and then brought it to a close in 1973 by going off the gold standard, Mr Obama can only achieve the changes he wants through persuasion.
Even then, he is unlikely to get everything he desires. In each of the four areas that Mr Obama wants to see progress, the president is likely to bump up against the realities of reduced US power.
Mr Obama has said he wants four things from the summit. First, he has called for a "robust" co-ordinated stimulus, most recently in an interview with the Financial Times. Countries such as Germany and France resent being told to run up large public debts in order to shield the world economy from the consequences of what they see as US mistakes.
Mr Obama has already indicated he would accept a form of words pledging "to do what is necessary", rather than concrete new commitments to more spending. "This is not a pledging conference," Michael Froman, the US senior official, for the G20, said yesterday.
Second, Mr Obama has called for an expanded scope of regulation. Here, he is likely to make more progress. Most developed economies, particularly in Europe, agree to the proposals that Tim Geithner, the US Treasury secretary, unveiled in Washington last week for an overhaul of US domestic regulation.
This would involve setting up systemic risk regulators that would regulate institutions not by what they are but by what they do - enabling them to regulate hedge funds and other non-bank institutions.
There is also agreement on the need to set up better capital adequacy rules and other technical reforms, much of which will take time to hammer out.
But even here, there is friction with the Europeans. Both sides recognise that the underlying impulse stems from a conviction that the US authorities disastrously mishandled the supervision of such markets leading up to the crisis and cannot be trusted not to do so again in the future.
It can be seen, for example, in moves to develop a more robust infrastructure for over-the-counter derivatives at the European level. The arguments given for this include the European home base of many participants in these markets, and the potential need for euro-denominated support of a central counterparty in a time of crisis.
The "soft power" of the US private financial sector has also been devastated by the economic turmoil. Under George W Bush, US officials used to urge countries such as China to embrace the likes of Goldman Sachs and Merrill Lynch and use them as engines of domestic transformation - an idea no one is advancing today.
Third, Mr Obama wants to retool the International Monetary Fund as the principal vehicle for assisting the developing world through the downturn.
The limits to US power were visible at a recent G20 finance ministers meeting where Mr Geithner agreed that the US would no longer monopolise the post of president of the World Bank and the Europeans would give up their control of the post of managing director of the IMF.
But the US will find it hard to get full European support for a radical reweighting of the IMF's voting shares to accommodate emerging powers, such as China and India - since most of the dilution would come at European expense. Nor is the US likely to get agreement for a tripling of the IMF's resources to $750bn (pound 525bn, euro 566.7) - again largely because of European opposition.
Finally, Mr Obama wants a concrete pledge forswearing protectionism. The first G20 summit last November promised much the same thing. But 17 of the 20 participants have instituted new protectionist measures since then, according to the World Trade Organisation.
Here though, the US is as reluctant as everyone else to make a genuinely binding pledge to avoid protectionism by, for example, giving the WTO new powers to crack down on offenders. Congress would be unlikely to accept such an implied restriction on US sovereignty, even while global realities are imposing new such restrictions with each passing week.
Copyright The Financial Times Limited 2009