Buoyed by rising approval ratings at home, Barack Obama will face his first serious test as an international leader in London today at the start of a five-nation European tour crammed with speeches, dinners and summits as well as one-on-one meetings with counterparts from around the world.
London may be the site of tomorrow's vaunted G20 meeting but Mr Obama, who landed at Stansted aboard Air Force One last night, has much else on his plate, including sit-down talks at Winfield House, America's ambassadorial mansion in Regent's Park, this morning with Russia's President Dmitry Medvedev and President Hu Jintao of China.
Nor will Mr Obama escape the thickets of British politics, taking breakfast along with the first lady, Michelle Obama, at Downing Street before private talks with Gordon Brown followed by a joint encounter with the press. Convention dictates that he breaks later for a meeting with David Cameron.
Mr Obama will go into tomorrow's summit aware of the resistance of France and Germany to any outcome overly emphasising the role of stimulus spending in responding to the global economic slowdown. In recent days, the White House has played up his willingness to accept a "both/and" approach featuring stimulus measures and greater regulation of the financial sector.
British officials last night said that Mr Obama had spoken to Mr Brown by telephone from on board Air Force One to "take stock" on the best way forward at the summit. Their conversation followed reports that France's President Nicolas Sarkozy might walk out of the meeting if the conclusions on tackling the economic crisis did not satisfy him.
Prepare for pomp when America's first couple depart Winfield House this afternoon inside the "Beast" – the armoured limousine we first saw on Pennsylvania Avenue on inauguration day – bound for Buckingham Palace for a private audience with the Queen before a royal reception for all G20 leaders and a working dinner hosted by Gordon and Sarah Brown at Downing Street.
The star turn in the circus that London will become for the next 48 hours, if not the actual ringmaster, Mr Obama will be playing to several audiences. For the people of Britain, he may be obliged to break at least for a few instants from his security bubble to touch flesh with "real people". Chippies and posh pubs within range of Regent's Park or Buckingham Palace should be on high alert.
But his first concern may be the American television crews, who will be relaying every smile and handshake of his European tour to audiences back home, where on his return he will face a tough budget battle with Republican and moderate Democrats on Capitol Hill.
For his supporters, however, this is the moment when Mr Obama can begin to repair a national image badly scuffed when European leaders separated from the previous administration of George Bush on issues from the war in Iraq to the treatment of prisoners at Guantanamo Bay and climate change.
A CNN poll showed 86 per cent of Americans expecting Mr Obama to do "a good job" on his first major trip abroad, while Mr Obama's overall approval rating in a Washington Post poll rose to an impressive 66 per cent.
Challenges lurking in relations with China and Russia include the way forward on halting Iran's nuclear ambitions and the alleged preparations for a new missile test by North Korea. Moscow and Washington, however, have both spoken of the opportunity for an improvement in ties that may be manifested by a joint statement on resuming steps to reduce their weapons arsenals.
Mr Obama is likely to emphasise what separates him from Mr Bush, including a revived commitment to combating global warming ahead of post-Kyoto treaty negotiations later this year in Copenhagen. Foreign policy will meanwhile dominate his meetings later this week in France, eastern Europe and Turkey. Most notably, he will need to sell to Nato allies his repackaged approach to Afghanistan and yoking the campaign to future policy on Pakistan.
On the fringe
* The Russian President, Dmitry Medvedev, has arrived from Germany where he consulted with Angela Merkel. When in London, in addition to Gordon Brown, he will see the Chinese and Australian leaders. Russia has a Pacific rim after all.
* Kevin Rudd, the Australian Prime Minister, will be in the thick of a whirlwind of meetings with six G20 leaders over the next three days.
* The feisty President of Brazil, Luiz Inacio Lula da Silva, will present a joint initiative for global financial reform with the Argentine President. It will have escaped nobody's notice that Lula conferred with President Nicolas Sarkozy on his way here.
* The most unusual meeting will be that of Prince Charles with Chinese President Hu Jintao. The Prince once described the Chinese leadership as "appalling old waxworks".