By Nick Assinder
Political Correspondent, BBC News website
Barring a last-minute political earthquake, Tony Blair looks set to win this week's crucial vote on his education reforms by a reasonably comfortable margin.
There will be a sizeable backbench rebellion, despite the concessions already offered by the prime minister which, he insists, have left the core of his proposals intact.
Blair has backbench opposition
But no one believes the revolt will be anywhere near big enough to defeat the bill, particularly as some of the leading rebels have now fallen into line.
A BBC Newsnight survey suggested that at least 39 rebels would rebel. It only takes 35 rebels for Mr Blair to need opposition support to win the vote.
So what is all the fuss about. Why are the prime minister and his Education Secretary Ruth Kelly devoting large amounts of their time this week talking to Labour MPs in a bid to win them over?
Why is this particular vote and rebellion seen as the most pivotal in Mr Blair's third term of office?
After all, the prime minister has weathered plenty of backbench revolts in the past without the walls of Downing Street crumbling.
And lastly, why has the prime minister deliberately timed his monthly press conference for the morning after the vote?
The simple answer to all three questions is that the prime minister himself made this single bill the "defining moment" of his third and final term.
Kelly is trying to win over rebels
In other words, this is the thing he wants to be remembered for long after he has left power.
He undoubtedly hopes the effects of his reforms will be so far-reaching, long-lasting and, ultimately, approved of that they will drown out the negative fallout from his decision to go to war on Iraq.
The crunch, however, is that he appears so determined to secure this legacy that he is prepared to achieve it on the back of a Commons victory handed to him by the Tory party.
He insists the bill, now including those concessions to his rebels, is a "Labour bill" and he would dearly love not to have to rely on Tory votes to get it through parliament - that's what all the cajoling and arm twisting of backbenchers is about.
Deputy prime minister John Prescott, himself a former doubter, told a meeting of Labour MPs that the party and the country would not forgive them if the bill was delivered on Tory votes
But if Tory votes is what it takes then, by the prime minister's own confession, he will live with it.
And that explains the timing of the press conference, the morning after the night before.
Prescott warned backbenchers
It is expected he will use the occasion to defend such a victory and bat off any suggestions he has lost authority over his own party and MPs and, even, that he should now stand down.
Of course, there is still enough time for that earthquake which might change the entire geography of this vote.
The Tories could change their minds and whip the rug from under (unlikely as they are doing enough damage by supporting it) or enough backbenchers could be persuaded to toe the line to ensure it really is a Labour bill.
But, barring those scenarios, it is likely that Thursday's press conference will be taken by a Labour prime minister who has been propped up by Tory votes.
And the full consequences of that are impossible to predict.