Ed Miliband's move to shake up the trade unions' relationship with Labour looks to be simultaneously his strongest and weakest moment as party leader.
Strongest because he is being bold and ambitious in seeking a radical set of reforms which, if accomplished, would transform and revive the Labour party's ailing membership fortunes.
Weakest because he was forced into pursuing these reforms by events which he initially tried to avoid confronting.
And also because the chances of success are slim. The trade unions are Labour's bankrollers and, while Miliband might persuade half of the affiliated unions to accept the changes, that will still leave a significant number of refuseniks.
By winning over half of the affiliated unions the party leader should hold enough bodies to control the issue in a national executive committee vote. The question then becomes: How will the remainder respond when Miliband presents them with a fait accompli?
It's true the unions do not hold all the cards. They would be wandering into the political wilderness. That was the choice made by the Rail and Maritime union many years ago; its left-wing firebrand leader Bob Crow might say what he likes, but he does so outside the umbrella of the Labour movement.
But they would also be depriving Labour of many, many potential party members and all the funding that goes along with them. The changes Miliband is seeking "could grow our membership from 200,000 to a far higher number", he said in his speech earlier. Not if he cannot win over the bulk of the unions.
A lot is at stake. Miliband is not providing any real answers about how he will persuade the union bosses to give up much of their existing influence.
So when he declares that "we're going to get these changes" - and stating on the record "I definitely want these changes agreed before the next general election" - he is placing his credibility on the line.
"I want this done as soon as possible," he said in the question and answer session after his speech.
Look at these two sentences and it's obvious where the problem lies.
"No one should doubt my determination to do this, but we do need to have some discussions now."
And: "It's always the case it takes some time for the dust to settle... but I'm convinced the right thing will happen."
Both those statements should have ended before the 'but'. They reveal a huge gap between Miliband's stated aims and what he can actually demonstrably achieve.
This is out of the ordinary. A politician of his status would usually bend over backwards to avoid leaving himself exposed to possible failure like this.
Miliband has chosen to take a big risk because the alternative - doing nothing - is too horrific to bear.
He would have faced months of mockery by David Cameron in the run-up to the next general election. Every jibe in prime minister's questions would have shown Miliband to be weak and undermined him in the eyes of voters and MPs alike.
Like a frightened animal trapped in a corner, prodded and goaded by his enemies, the Labour leader is now decisively hitting out.
He is taking on the unions out of necessity - and success is far from guaranteed.
He is also taking on the Tories over the one area of political reform where Cameron's party is relatively weaker - second jobs. Most, but not all, of the MPs earning most from their second jobs are Conservatives.
Targeting them will also frustrate a number of Labour MPs. That worry is trumped by the need to have something, anything, with which to come back at Cameron across the despatch boxes.
The continued opportunity to top up their salaries isn't what should be worrying disgruntled Labour backbenchers, though.
The last time the relationship between the Labour party and the trade unions changed in this way was in 1927, when the Conservatives moved decisively against the unions. Labour's funding dropped by nearly a fifth as a result.
A similar result this time around would make it much harder for Labour to prevail in the critical marginal constituencies which will decide the next general election.
So Labour MPs watching their leader embarking on his desperate, radical course of action should be bothered about more than just second jobs. What should really be keeping them awake at nights is the possibility that Miliband might actually succeed.
What should really be keeping them awake at nights is the possibility that Miliband might actually succeed.