For all these reasons it's tempting to personalise, at Ms Harman's expense, the row over the cut in lone parents' benefit. It is a temptation which several of her critics, in the press as well as in the ranks of Labour MPs, have found impossible to resist. But it is based on a serious misapprehension. The policy she defended in the Commons yesterday is very far from being hers alone. The cut is directly in line with the decision of Gordon Brown to stick rigidly to the spending limits set by his predecessor. Some leading critics - such as Ken Livingstone and Chris Mullin - have not shrunk from acknowledging this; others have. It is much more fashionable - and perhaps a little less risky - to criticise Ms Harman than it is to criticise the Chancellor and the Prime Minister. But the decision to stick to Ken Clarke's spending limits for two years was announced before the election; it formed part of Labour's programme, and it was probably part of the unprecedented economic credibility that helped to deliver Labour its landslide on May 1. It's true that the Chancellor has juggled some figures to inject more cash into health and education. But that was to meet cherished and, during the election, stated priorities. By contrast the lone parents' cut played directly to both Brown's and Tony Blair's desire - wholeheartedly shared, it should be admitted, by Ms Harman - to see the poor, including poor lone mothers, lift their prospects by taking jobs rather than stay at home. Part of her case has been that by taking jobs, including part-time jobs, lone parents would, thanks to the in-work benefit of Family Credit, be better off - by an average of pounds 50 per week - than if they weren't in jobs. In that sense it was an important and highly symbolic part of the welfare to work programme. (So to are the two concessions Ms Harman and Mr Brown have made - bringing the programme to get lone parents into work forward to next April and providing pounds 300m of lottery money for child care.) Finally it was also, perhaps, in line with Tony Blair's social and moral agenda - through trying to discourage young women from regarding single motherhood on benefit as a realistic means of livelihood. There were - and are - valid arguments to be levelled at the policy; not least the question of whether the cuts should have applied to new lone parents of children under five. And while the cuts apply only to new lone parents, what of single mothers who take short-term jobs and then are forced back on to income support? As new claimants they would now be subject to cuts of up to pounds 11 per week. Ministers are adamant that even lone parents taking short-time jobs will still be better off over the year; nevertheless some of these arguments were well worth having out.
But a serious problem is that the parliamentary left didn't focus on them until it was too late. When on 22 July the Liberal Democrats sought to amend the Bill reducing child benefit for lone parents, the present dissidents (Ken Livingstone, Diane Abbott, Audrey Wise, Chris Mullin, among them) voted with the Government against the amendment, despite a long and eloquent speech by the Liberal Democrats' social security spokesman Steve Webb criticising the cut. This has added to the suspicion that at least some of the putative rebels decided to focus on the issue much later, possibly because student fees had failed to live up to expectations as the lightning conductor for discontent.
In other words this may have been as much about testing left-wing strength as it was about concern for lone mothers. Which means that any putative rebel can only protest by voting down - or abstaining - on the whole Social Security Bill, a large part of which is an entirely welcome simplification of the benefit claims system. Some in the Government didn't handle the issues as well as they might have done. In particular it is distinctly odd that at least some government whips appeared to have given tacit encouragement to Mr Mullin's confidential round robin to Mr Brown. Whoever encouraged them to do this, it was not Ms Harman. Maybe it was just a way to minimise the level of public protest and persuade dissidents not to sign an open motion attacking the cuts. But it must have led some of the signatories to feel that they were on a winner.
Which they are not, and to be realistic, never could have been. This has now become an issue of the Government's credibility. If at the first signs of revolt - and those actually abstaining in the crucial division may be as few as a fifth of those who signed Mr Mullin's letter - ministers buckled, it would have gravely weakened Brown's claim to fiscal prudence. Every promise of responsible economic management would come under scrutiny, not least in the markets. This isn't perhaps, the issue most ministers would have chosen. Suddenly the Government's New Deal for lone mothers has become frighteningly real: a great deal hangs on it. If it is shown to work then it will be much easier to defend the cuts. If it doesn't - and the evaluation promised by Ms Harman will have to be serious - then ministers will have to rethink, perhaps as early as next year. But for the time being Mr Brown and Ms Harman have made all the concessions they are going to. And they have no choice.
Ms Harman, by nature a tough political survivor, may be taking the flak for now; but there is a lot more at stake here than the short-term popularity of a single minister.