The head counting has begun in earnest. And the way the numbers fall will be no small matter of interest for the Prime Minister.
If the Civil Union Bill is defeated in Parliament tomorrow afternoon, it will be an embarrassment for Helen Clark.
Her authority will suffer a dent - not because she backed the measure, but because she will be on the losing side. And on the losing side because some of her own MPs voted against the bill proceeding.
Normally, prime ministers steer well clear of conscience issues, casting their vote with nary a comment.
But Helen Clark has increasingly found herself being forced to defend the bill, which establishes an alternative to marriage for both heterosexual and homosexual couples, partly because it is Government-sponsored rather than a private member's measure.
If the bill is thrown out on its first reading - and the vote will be close - the Government will have egg all over its face. It will have brought a highly contentious measure before the House lacking the numbers to pass it, unnecessarily copping a deluge of criticism it can well do without.
Presuming the bill passes its first stage and goes to a select committee - and Helen Clark and the bill's supporters will be lobbying doubters to allow it to get that far at least - she can breathe easier.
The legislation will have obtained a degree of "buy in" from Opposition parties.
Some National and Act MPs will vote for the bill. Some Labour MPs will vote against it.
Ownership of the measure will consequently be more widely shared across Parliament.
There will be more negative headlines during the subsequent select committee hearings. But the Government should be able to progress the bill fairly rapidly.
Private members' bills - the most notable recent example being the Prostitution Law Reform Bill - are debated only every second Wednesday. They consequently take many months - sometimes more than a year - to get through the House.
The Civil Union Bill will be law before the end of the year. Once the first flurry of gay couples have cemented their civil union, the fuss should subside.
The Government's headaches have instead come in the lead-up to the bill's introduction.
It has done a poor job of selling the measure, allowing United Future's Peter Dunne to define the argument as being about undermining the sanctity of marriage rather than, as the Prime Minister says, about choice, fairness and equality.
The Government should have foreseen that one of the minor parties would seize on the bill as a means of generating profile.
However, the Government's hesitancy followed the backlash against so-called political correctness, exacerbated by the coincidental furore over same-sex marriages in the United States.
National, for one, has seen the bill as an opportunity to paint the Prime Minister, who has declared a personal preference for a civil union rather than marriage, as offside with mainstream thinking.
She and her ministers have been criticised by allies for not having the courage of their convictions and legalising gay marriage, while opponents say civil union is marriage in all but name.
The divergence has allowed the Prime Minister to claim the Government is treading a middle path.
In reality, she is struggling to save the measure from extinction.
She has wielded every argument she can think of, while preparing her defences in advance of possible defeat.
She has pointed to examples of overseas countries which have likewise legislated civil union or partnership rights for same-sex couples.
She has noted the work to outlaw discrimination against same-sex couples began during Doug Graham's tenure of the Justice portfolio - thereby seeking to implicate National even though his work had nothing to do with civil unions.
She has firmly drawn the line against the legalising of gay marriage.
Labour's gay MPs have been told to take a back seat to prevent critics accusing the Government of pandering to the "pink vote".
And she has stressed this is ultimately a conscience measure and thus Parliament's decision, not the Government's.
It hardly adds up to a rip-roaring celebration of the measure's intent.
But both Helen Clark and David Benson-Pope, the minister in charge of the bill, have kept their nerve, not least because the left faction in the Labour caucus will be furious if they buckle.
Labour has been guilty this year of appearing to be merely poll-driven and not standing by its core vote.
Not on this occasion, however.