By Nick Assinder
Political correspondent, BBC News website
Peter Hain's attack on President Bush and the Iraq war will undoubtedly embarrass Tony Blair on the day he meets US Secretary of State Condoleezza Rice in London.
But, as the campaign to replace John Prescott as deputy Labour leader intensifies, he can expect more - candidate Hilary Benn, for example, has also said it is time to admit to the mistakes made in Iraq.
Mr Hain is bidding to be deputy leader
The Northern Ireland and Wales Secretary's remarks, in a New Statesman interview, are the latest move in his campaign and are seen as an attempt to position himself and appeal to the grassroots party members and others opposed to the war and the Republican administration in the US.
As far as that goes, he has almost certainly selected the right target, even though it has been pointed out he voted for the war - which, he explains, was because he believed threat from weapons of mass destruction existed.
He has previously been critical of the president and the neo-conservative agenda which he now claims has been "kicked into touch" by the American electorate.
It was always likely the deputy leadership campaign would see some of the competing candidates expressing views out of step with the leadership.
But Mr Hain's criticisms go further than an attack on the US - they are also being seen by many as a thinly veiled assault on Tony Blair himself.
That is not simply because Mr Blair is as tied to the war as the president.
It is because of a very pointed remark in the interview in which Mr Hain appears to be attempting to explain Mr Blair's position.
He said the problem for the government had been to "maintain a working relationship with what was the most right-wing American administration - if not ever, then in living memory".
Mr Blair is seen by some as too close to Mr Bush
Many on the Labour benches and amongst grassroots activists believe Mr Blair went very much further than maintaining a "working relationship" with the president.
They believe the prime minister signed up to the Bush, neo-conservative, unilateralist agenda and was too enthusiastic in his support for the Republican president.
They point to the relationship former Labour prime minister Harold Wilson maintained with Democrat President Lyndon Johnson when he refused to send British troops to Vietnam.
It may have put huge strain on the transatlantic partnership, but it did not fracture it.
The fact that Mr Hain also referred to his former ministerial boss, the late Robin Cook, was also seen as a further signal of where he is coming from.
The interview has led to questions about whether the prime minister's authority has now evaporated to the extent he has no power to stop such attacks or discipline those making them.
Or whether he is simply stepping back from the deputy leadership campaigning to give the candidates breathing space.
His official spokesman, for example, refused to get drawn into the debate, saying Mr Hain's remarks had been made in a "political context" - as a civil servant, the spokesman is barred from involvement in overtly political issues.
Whatever the motivation, though, it is a certainty there will be much more of this sort of positioning before the deputy leadership campaign ends.