By Paul Reynolds
World affairs correspondent, BBC News website
President Bush attends the annual US/EU summit in Vienna on Wednesday in the shadow of Guantanamo Bay and Iraq, yet determined to present a newfound unity over Iran as the main theme.
President Bush is likely to be pressed over Guantanamo Bay
Even the UK has joined the chorus calling for the closure of the US military camp in Cuba.
But if the EU and the US have come apart over that, they have come together over Iran - and that perhaps is a pointer to a future of greater multilateralism.
Mr Bush's National Security Adviser, Stephen Hadley, said that the president wanted to highlight the "united front" over Iran, and saw this trip as "an opportunity to reaffirm the strong relationship between the United States and the European Union."
When senior officials say things like that, you know that something needs repairing. In this case, transatlantic ties.
It is astonishing how much the relationship between Europe and the United States has deteriorated since the French newspaper Le Monde declared after the attacks of 9/11: "We are all Americans now."
From the high days of that sympathy, Mr Bush has become an unpopular American president in Europe.
Despite a recent bounce in Iraq - with the new government and the death of the al-Qaeda in Iraq leader, Abu Musab al-Zarqawi - he is a weakened figure.
Mr Bush will meet senior European Union officials
The end of an era is in sight, and a power struggle is under way in the administration with Secretary of State Condoleezza Rice - who will be with Mr Bush in Europe - increasingly getting the upper hand as she reasserts the power of diplomacy over the power of arms.
Not that the EU is in great shape itself. It is wallowing around in limbo after the failure over the constitution and has no real idea of how to go forward.
It has found some common ground in criticism of the US, and the Austrian Chancellor, Wolfgang Schuessel, is expected to raise the Guantanamo issue.
Mr Bush will no doubt argue that he would like to close the camp and is waiting for a Supreme Court ruling about the legality of military tribunals.
However, even if the court allows the tribunals to go ahead, the bulk of the 500 or so prisoners there are unlikely to face them - only a handful of tribunals have been announced so far - as there is so little useable evidence against them.
Sharp questioning of the president would be in order to find out what might happen to them.
Some analysts feel that the dynamic of the transatlantic relationship has changed in the second Bush term.
John Palmer of the European Policy Centre in Brussels said: "What has changed in Vienna is that the Europeans are clearer about the dramatic limitation of the reality of the US as a superpower. It has not escaped their notice that the US had to turn to the European strategy for Iran. The Europeans resent an overbearing hyperpower but are aware of the problems of an implosion of worldwide US power and are worried at the implications for both the future of real multilaterism and potential isolationism by the United States."
On these annual get-togethers, which last barely a morning and a lunch, the US president must sometimes be rather bemused about whom he is meeting. Mr Bush might wish that his friends Tony Blair and Angela Merkel were there.
But this is not an occasion for European heads of state and government.
Instead, Mr Bush must meet the current EU president, who is in office for only six months, the Commission President Jose Manuel Barroso, the EU's Foreign Policy chief Javier Solana, the Foreign Affairs Commissioner Benita Ferrero-Waldner and Peter Mandelson, the Trade Commissioner.
A large element of the agenda deals with the main relationship between the EU as a group and the US - trade.
The heavy lifting of diplomacy on world events is really done at government-to-government level because the EU has only a minimalist collective foreign policy. Britain, France and Germany, for example, handle the Iran talks.
The current big issue on trade is the state of the world trade talks, which is parlous.
The EU and the US have squabbled about how to cut agricultural subsidies yet have common cause in getting the developing world markets, in Brazil and India for example, opened up more.
Look for some talk on this issue, if no breakthrough. The expectation currently is for a world trade deal at the lower end of ambitions.
There will be a small success in that the two sides have agreed to fight together against pirated goods, but there is a developing row over the US insistence on visas for citizens of some of the newer EU states and that will prove prickly.
Mr Bush will no doubt feel relieved when the EU talks are all over and he goes to Budapest for the commemoration the next day of the fiftieth anniversary of the Hungarian uprising.