Tony Blair and Charles Clarke knew from the outset that they would have to go out and sell their controversial plans to introduce variable tuition fees.
Has he done enough to convince the doubters?
After all, 155 Labour MPs had put their names to a motion opposing the policy even before the Higher Education Bill had been published.
The prime minister and the education secretary have spent the best part of January trying to win over these backbenchers.
Both Mr Blair and Mr Clarke had insisted there would be no significant concessions once the Bill was published.
Impact of the new system to be reviewed after three years
A clause in the Bill to ensure fees do not rise about £3,000 for two general elections
The new grant for living costs to rise from £1,000 in 2004 to £1,500 from 2006
The £1,200 fee remission for poorer students may be offered as an up-front grant
Anyone still in debt after 25 years will have their loans written off
All students will qualify for the interest-free loans to pay fees
And it does seem that despite talk of fresh concessions, there has been little substantive change.
Before it was published some MPs feared that some students would be denied the opportunity to get interest free loans to pay for their courses.
But the Bill made it clear that all students, irrespective of their parents' income, would qualify.
Similarly, there were concerns some people could spend their entire life repaying the cost of their university education.
But under the terms of the Bill, anyone still in debt after 25 years would have their loan written off.
Many MPs have voiced concerns that the introduction of variable fees would be the first step towards allowing universities to charge what they like.
Mr Clarke said he would ensure that no university could charge more than £3,000 until after two general elections - effectively six years.
HOW THE NUMBERS ADD UP
Vote takes place at 1900GMT on Tuesday
The government has a majority of 161
If all opposition MPs vote against, it needs 81 Labour MPs to rebel for plans to fall
ABout 150 Labour MPs signed a motion opposing fees
Tony Blair says his authority is on the line with the vote
He has now said that this verbal commitment will be written onto the "face of the Bill".
As the Bill was published, he also promised extra money for poorer students.
The new grant aimed at covering their living costs would rise from £1,000 in 2004 to £1,500 from 2006.
And Mr Clarke has held out the prospect of the promised £1,200 discount on fees for poorer students being offered as an upfront grant.
These measures are aimed at luring rebel MPs back onto the government ship.
They seek to do so without compromising on the key area of variability - which allows different universities to charge different fees for different courses.
Whether or not enough has been done, will become clear at about 1900 GMT on Tuesday in a vote Downing Street says is still "too close to call".