Whether on Iraq, health reorganisation, schools reform or civil liberties, the relationship between Labour and millions of progressive voters has become sour and distrustful. It flourished in the mid-1990s and underpinned our landslide victory in 1997. Now fractured, it puts the party's chances of a historic fourth-term victory at risk, allowing the Conservatives back into power.
George Bush's two terms in the White House graphically demonstrate the danger. The Tories, fronted by a fresh face and projected with slick spin, promise a break with a deeply unpopular party's nasty past. Ominous echoes of the "compassionate conservative" governor of Texas as he campaigned for the US presidency seven years ago.
But scaring progressive voters with the image of David Cameron crossing the threshold of No 10 won't win Labour the next election. Instead, we need to understand why it is that - despite all the achievements of the past ten years - so many of those who enthusiastically supported us in 1997 are now so deeply hostile.
The progressive coalition that Labour so successfully assembled in 1997 has splintered because we have been careless, indifferent and, at times, needlessly offensive to the concerns and values of too many of our natural supporters.
This has not simply been a sin of omission. Instead, it has appeared a conscious strategy. Too often, the credo has been that winning the centre ground - itself unquestionably vital for electoral success - is, in part, achieved by Labour defining itself against the values of progressive Britain. This has always been a false choice. We proved in 1997 that it is possible to win both Middle Britain marginals and Labour heartlands; indeed, since then, we have lost support in both simultaneously.
The chase for headlines in the right-wing press is based on a fundamentally flawed calculation: that progressives have nowhere else to go but to vote Labour. This is a dangerous assumption. In 2001, some of those who had voted Labour four years earlier simply stayed at home. Only Tory weakness and a very low turnout prevented serious electoral damage.
In 2005, however, substantial defections from Labour to the Liberal Democrats not only produced losses from Cambridge to Cardiff Central, they also handed the Conservatives - often without raising their own vote at all - more than 30 seats. Labour ended up with a shaky win and a vote, at just 36 per cent, lower than when we lost to Margaret Thatcher in 1979.
If this strategy was electorally risky in the face of a string of overtly right-wing and weak Tory leaders, it could be near-suicidal when we are up against today's reinvigorated Con servatives. Cameron's sidling up to progressive causes such as civil liberties, inequality and climate change is entirely synthetic, all spin and no substance. Nevertheless, it is cunningly calculated to make the Tories appear a whole lot less threatening - if not necessarily attractive - to large numbers of those who were willing to rally around Labour in 1997 in order to evict John Major from No 10. They might well not vote Tory, but equally they might not vote at all if the prospect of a Cameron victory doesn't overly bother them.
But flirting with the anti-liberal prejudices of the right-wing media is counterproductive in another way. When some at the top of the party have seemed at best sullen and at worst downright hostile to our progressive record, what chance do we have of asking people on the left to give us any credit for it?
The Human Rights Act is a case in point. Sometimes we have seemed more concerned with colluding in fantasies and fallacies than with robustly and proudly defending legislation that embodies our commitment to human rights. This has left the door open to Tory right-wing attacks; a stark contrast with other parts of our record that have been solidly defended, such as the minimum wage, civil partnerships, or the creation of devolved institutions in Scotland, Wales and London, all of which the Conservatives have been forced to accept.
On the fight against terrorism, everyone understands that, after 9/11 in New York and 7/7 in London, we need to have a serious debate about the balance between liberty and security. But we have contrived, through government rhetoric and spin, to appear casual about, or even indifferent to, civil liberties, which itself undermines the fight against terrorism. We may not have encountered so much hostility and difficulty with our anti-terrorism laws if we had led the debate in a manner that suggested we cared both about the security of the country and the civil liberties of those who live in it, rather than appearing to suggest that the former can be achieved only by sacrificing the latter.
Gordon Brown's recent suggestion that any further anti-terrorism powers must be accompanied by stronger judicial and parliamentary oversight offers the prospect of a welcome new approach.
The war in Iraq has, of course, also played a significant part in fracturing the progressive coalition. Like all my fellow deputy leadership candidates, I voted for the war. It does nothing to rebuild trust in politicians if, at the moment when it would be most politically expedient to do so, I followed the example of two of my colleagues, renounced my vote and tried to write myself out of the decision. I know only too well the damage to Labour and the anger the war has caused, not only on the doorstep, but over family dinners and in conversations with long-time friends who have felt unable to remain in the party.
Rather than trying to wriggle out of personal responsibility for our decision, I think people should ask that those they entrust to make decisions learn from those decisions. The lessons of Iraq are that military power alone is no substitute for winning the battle of hearts and minds, and that we need to reform and strengthen the capacity of the UN, Europe and other multilateral bodies, including the Arab League.
It is also vital that the left and wider progressive opinion does not, because of Iraq, abandon the internationalism that first brought me from the struggle against apartheid into the Labour Party. An isolationist foreign policy, usually favoured by the right, would not have saved the people of Sierra Leone from savage butchery, nor Kosovans from genocide. The ongoing suffering of the peoples of Burma, Zimbabwe and Darfur underlines why international intervention to protect democracy and human rights must always be high on the left's agenda. The failure to resolve the continuing, and often bloody, impasse between Israelis and Palestinians remains the principal failure of global diplomacy.
Forging a progressive internationalist foreign policy built on these lessons - coupled with a renewed drive to promote global social justice and tackle climate change - is the way to win back Labour support among progressive voters, by renewing confidence that we share the same values.
Domestically, we must prioritise tackling inequality. Top of our agenda must be the lack of affordable housing for rent and purchase, the need to ensure the proper enforcement of employment rights in the disturbing twilight world of agency, temporary and subcontract work, and a major push for free universal childcare. Coupled with greater individual empowerment, strengthened local government and finishing the job of democratic renewal - redistributing not just wealth, but also power - the drive against inequality should be the golden thread that runs through our entire agenda.
We leave our progressive flank unguarded at our peril. How on earth did we allow Cameron to steal a march on green issues, given the government's international and European leadership on climate change? The truth is that we failed for too long to prioritise the green agenda as the core Labour issue it so palpably is. If the Tories can attempt to steal progressive voters from us when they have barely any green policies, no record of prior commitment and, until very recently, zero credibility, then no territory is safe. We must challenge them with a red-green agenda that combines social justice and environmental protection, tackling climate change but ensuring that the responsibility for doing so is fairly shared.
However expedient their motives, the Conservatives have finally realised the electoral importance of Britain's progressive majority. A decade ago, so did we. It's now high time we did again. And that means we need to stop insulting it.
Peter Hain, Secretary of State for Northern Ireland and Wales, is a candidate for Labour's deputy leadership
His manifesto is available at http://www.Hain4Labour.org