Ed Miliband should have seen this trouble coming. Indeed, he did. Having won the Labour leadership by a trade-union ramp against party members and MPs, he knew he had to prove he was not the unions' creature.
Thus one of his spin doctors, Tom Baldwin, briefed the newspapers before the 2011 Labour conference to say that Miliband would announce rule changes to cut the trades unions' 50 per cent share of the vote at conferences in future. Only it never happened.
A few days later, we were told Ed Miliband would be proposing "the biggest change to the party's structures for 20 years", but the plan now consisted of signing up a new category of "registered supporters". The idea was that, if more than 50,000 signed up nationally, they would be given a tiny share of the vote in leadership elections. This would dilute union influence, but hardly at all, and it would equally infinitesimally dilute the influence of party members and MPs. There are still two web pages where you can sign up, but nothing has been heard of the scheme since.
That was Miliband's attempt to anticipate the inevitable attack on him for being in hock to the sectional interests of the unions, the two biggest, Unite and the GMB, in particular. A failed attempt, two years ago, to dilute the grip of the unions on Labour Party policy. He was thinking of returning to the question at this year's annual conference, with some kind of defiant declaration of independence, but now it is too late. A routine shenanigans over the selection of a Labour candidate to replace Eric "Street Fighting Man" Joyce in Falkirk caught up with him.
So when the Tory attack was unleashed by David Cameron in the Commons last week, in one of his least prime ministerial and most effective performances, the Leader of the Opposition crumpled. To every question Miliband asked, Cameron replied, "Unite" and "Len McCluskey", the union's leader.
Having refused to accept the resignation of his election co-ordinator, Tom Watson, the day before, Miliband had another conversation with him. As a result, Watson resigned from the Shadow Cabinet. Watson is a paradoxical politician: the Brownite assassin whose resignation as a minister in 2006 precipitated Tony Blair's departure, who is also an engaging and principled MP. He is a fixer credited with supernatural powers, yet he has been unable to fix a high position for himself. He wanted to be deputy leader of the party at one point, but is a backbencher again.
He resigned because he is a friend of McCluskey and he was involved in Unite's attempt to influence the Falkirk selection. In his resignation letter, he said that he hadn't seen the report of the party's investigation into allegations of sharp practice, but he believed "there are an awful lot of spurious suppositions being written". Watson seems to have seen more clearly than Miliband that he was a liability, and resigned when he should have been sacked – just as, seven years ago, he resigned before Blair could sack him.
Watson's departure is a reminder that the Blair-Brown divide has yet to heal. He complained in his resignation letter that other members of the Shadow Cabinet had been briefing journalists against him. It is worse than that: several have recently been in to see Miliband – not just to complain about his toleration of Watson, but about their feeling that the party is "drifting".
"On the economy, immigration, welfare and Europe," one shadow minister said to me last week, "we are losing four-nil."
But the crisis of party organisation is fundamental. The clique that runs Unite wants to put "working-class", "left-wing" candidates into the 41 Labour seats it has identified, by which it means candidates who reflect its unrepresentative ideology. To the extent that it succeeds, it will tilt the party away from the more centrist approach that even Ed Miliband knows is its best chance of winning.
It is already too late for Miliband to make much difference to which candidates are selected for the election. And it is too late for him to shake off damage done by his failure decisively to act against the undue influence over Labour of the leftists who run the main unions. If he thinks McCluskey is a problem, wait until he retires and is replaced by the even more anti-Labour Mark Serwotka.
Miliband needed within months of his election as leader to demonstrate his independence. He could, say, have opened up the choice of Labour candidates to primary elections among Labour supporters. There are all sorts of objections to US-style primaries: they are expensive for parties to run, and the rich and famous have a big advantage. But, as a Labour friend of mine said, observing the quality of the current parliamentary party, "What's wrong with rich and famous?"
It is, above all, too late for Miliband to recover the initiative. He belatedly announced that selection rules would be tightened to prevent unions or anybody else "buying" party members without their knowledge, which was already against Labour rules. He will unveil all manner of cosmetic changes to make it look as if he is standing up to McCluskey. But this is reacting to events, not leadership.