Everything hangs on Peter Robinson, the DUP leader.
With his agreement there can be a deal, without it there will be none. He is the pivot on which success or failure hangs.
History has cast him in that role. As the leader of the largest party he has an effective veto on progress. Sinn Fein also has a veto but it has already signalled that it is broadly satisfied.
On Christmas Eve, Sinn Fein's Ard Comhairle mandated their negotiating team to cut a deal, which could be ratified at a later Ard Comhairle meeting. Since then Martin McGuinness, the Deputy First Minister (below), has said that it would be "a terrible embarrassment for politicians, for the process, and would clearly show a lack of leadership qualities in terms of facing up to these very difficult challenges", if a deal could not be done.
The onus is now on Mr Robinson to decide.
Last night the White House increased the pressure with a statement calling on our political leaders to make "the compromises necessary to conclude an agreement now, one that would help heal the divisions that continue to stand between the people of Northern Ireland and the future they deserve".
Mr Robinson is a man who relishes pressure. In negotiations Mr Robinson takes the view that the more pressure you are under the stronger your position is and the more chance you have to get what you want from those pressurising you.
To have the White House, the nationalist parties and the British government all wanting a defined result from him increases his leverage and he can be expected to explore the possibilities that present themselves until the last moment.
So far he has been playing his cards close to his chest, tantalising other parties and governments with the prospect that he may agree but asking for more concessions to do so. Yesterday he said "there's a large part of the document I could readily bring to the party, there are other elements that render the rest unworkable".
The big question in the minds of others is whether he has the courage to close a deal that is less than perfect from a unionist point of view. Is he prepared to take flak? Is he prepared to risk giving an issue to rival unionists which they could use in next May's elections?
He has never had to make such a call on so great an issue before, and the signs are mixed.
Mr Robinson was central to negotiations on the St Andrews Agreement which brought the DUP into government with Sinn Fein. Yet he didn't carry the responsibility for St Andrew's; that task fell to Ian Paisley who was leader of the DUP at the time.
The prize was governmental power, but some question whether Mr Robinson could have taken such a bold and risky move had he not been shielded from internal criticism by the massive presence of Dr Paisley. It has been argued that Mr Robinson is more of a skilled political manager, who governs by focus groups and listens carefully to feedback, than a visionary leader who can take the risks necessary to bring his party to a new place. His recent decision to pull out of a deal with Sinn Fein on a peace centre at the Maze/Long Kesh was one recent instance where he changed direction after getting negative feedback on a bold decision.
Against that it can be said that, as leader, he took the decision to devolve Policing and Justice to Northern Ireland despite criticism from other unionists.
He was vindicated in that.
Today the stakes are higher still. The pressure puts Mr Robinson in a position to show leadership or the lack of it, and perhaps to define his place in the history books.
Much of the blame or the glory for what happens will fall to him.