Barack Obama has warned Ed Miliband that he can only win the next election if Labour embraces a more optimistic vision for Britain's future.
In talks between the two centre-left leaders last week, the US President set out the blueprint for inspiring British voters at a time of anxiety about the state of the economy.
During a 40-minute meeting at Buckingham Palace, President Obama and Mr Miliband discussed the shared challenges facing progressive parties on both sides of the Atlantic. The President in particular stressed the "importance of having an optimistic sense of national mission".
There has been growing unease among some senior Labour figures that, in opposing the coalition's spending cuts, the party risks being seen as relentlessly negative.
Mr Obama's soaring oratory most famously captured the American mood with his "Yes We Can" slogan, which swept him into the White House in 2008. It was a theme to which he returned in his Westminster Hall speech to MPs and peers on Wednesday, when he spoke of having "faith in the promise of tomorrow".
Douglas Alexander, the Blairite shadow Foreign Secretary who joined the Obama talks with Hillary Clinton, the US Secretary of State, insisted: "Ultimately, Labour wins by offering a better tomorrow and not a better yesterday."
In an interview with The Independent on Sunday, Mr Alexander made clear that Tuesday's meeting built on the tradition of Labour and the Democrats working together. "We talked both about how to frame and secure a progressive future in tough economic times, how do you give people the prospect of a better life, productive work, more opportunities, amid all the challenges facing the economies of Britain and America today. The strength of our ties with the Democrats remains strong and is very useful to Labour rebuilding."
There was also a warning that Labour cannot "appear in denial of the scale of the challenge, or offer simply a return to a better yesterday".
It is not the first time Labour has looked across the Atlantic for inspiration. In the mid-1990s, Gordon Brown and Tony Blair met a young Bill Clinton, to share high-minded ideas on building a progressive politics and exchange more lowly tricks for use in campaigns. Mr Alexander said these included how to establish a war room "so that if your opponents tell lies you can get the truth on the record pretty quickly", and the use of soundbites "to distil down a complex political message in a few seconds". Such techniques became synonymous with New Labour.
Striking a more upbeat tone will be vital if Mr Miliband, who married his partner Justine Thornton on Friday, is to secure victory at the 2015 general election. There are already mutterings in Labour ranks that this summer it is crucial for him to set out how he will win back votes in the swing seats that decide elections.
In the most recent Independent on Sunday/ComRes poll, only 22 per cent of voters thought Mr Miliband had proved a good Labour leader, one point more than those impressed by Nick Clegg as Lib Dem chief.
Labour strategists admit it will be a tall order to return to power within a parliament. But they believe the nature of the coalition is "speeding up the ageing process" of the Government, with policy rows, ministerial scandals and difficult local elections adding to the clamour for change.
Despite pleas from some in the Labour Party to do more to address the failings of the last government – including the economic crisis – when he returns from his honeymoon after the Commons recess, Mr Miliband is expected to make a series of speeches insisting that Labour must "own the future".