Opinion by Political Reporter Patrick Gower
Whether John Key says "I do" or "I don't" to same-sex marriage will decide whether or not the bill passes.
The Prime Minister's conscience is just one vote of 121 votes, but will be a critical lead to other National MPs.
As we saw yesterday, many of them would prefer to run than answer questions about gay marriage.
At the moment, Key's position is he will support the bill past its first reading. We don't know yet if he will vote against it at the third and final stage - like he did with Civil Unions. In that case, Key said he was acting on the wishes of his Helensville electorate.
So Key's "I'll support it to its first reading" is miles away from Obama's "I think same-sex couples should be able to get married".
Even if Key agrees with Obama, he may yet decide to go with the wishes of his conservative Helensville electorate and vote against same-sex marriage.
Key's branding and political power are so strong that if he backed out, a lot of the "undecided" National MPs would be empowered to as well.
On the flip side, if Key goes for it, they will be empowered to do the same.
Put simply: lots of the National MPs will do whatever Key does.
At the moment the numbers are pretty close. Key himself has acknowledged it's a conservative Parliament.
It would just take the rump of the National Party, John Banks, the NZ First guys and a few conservative Labour MPs to vote the bill down.
On the other hand, Key and National may want to look liberal; the party has just taken up the idea of same-sex adoption. Going for the bill could help Key in the centre-ground.
And that, of course, would open up room on the right for, guess who? The Conservatives leader Colin Craig.
National need a governing partner don't they?
By making a play for same-sex marriage, Key could just open the way for the partner he needs in 2014.