Who will succeed David Trimble? It is not the question of the moment. But it might fast become the question uppermost in the minds of Prime Minister Blair and Taoiseach Ahern.
Both men headed home last night, plainly exhausted by their longest week. They were clear they had put in place a solution which would enable the creation of an inclusive executive, and secure total decommissioning by the IRA. And, despite immediate disappointment, they travelled hopefully - reasoning that the Ulster Unionists must surely come to see their wisdom, take the risk and grasp the prize.
But will they? While Mr Trimble gave few clues as to his next moves, assorted spinners from the British, Irish and nationalist camps were happy to speculate he had little choice but to go back to his party and sell this "last chance" deal. Indeed, one SDLP source (seemingly convinced Mr Trimble and deputy John Taylor were already "on board") ventured that the unionist community "simply won't allow the backwoodsmen to reject this". With Drumcree and God knows what mayhem to come in the days and weeks ahead, this betrayed a touching (if unconvincing) faith in the greater good sense of the unionist-voting public.
Slightly more cautious (and apparently forgetful of the precedent his own party set at Hillsborough) a Sinn Fein spokesman volunteered: "He'll take a leaf out of our book and consult the party." But of course that, to Sinn Fein's mind, is where the comparison stops. Their pre-Easter luxury in rejecting the joint declaration by Mr Blair and Mr Ahern seemingly isn't available to Mr Trimble on this occasion. "Whatever way it goes," said the SF spokesman, "he's got two weeks until the British government has to implement this." The same message was subsequently hammered home to this correspondent by a leading member of the SDLP delegation.
Expressing confidence that Mr Trimble would sell the deal to his party, I gently inquired if he might be given rather more time in which to do so. Absolutely not, was the reply: "This is now, this is now." It is indeed, and it is prudent at this point to set aside the hype and calmly address what has actually occurred here.
Mr Blair's "absolute deadline" has come and gone. Undaunted, the "seismic shift" he discerned in republican thinking drove him on in a further dramatic bid to make the historic breakthrough.
Despite the bullying and the charm, the hostile briefing and the sweet talk, he failed to convince the Ulster Unionists of his analysis of, or the superiority of his insight into, the thinking and intentions of Sinn Fein and the IRA.
And while the prime minister thought to bank the progress made, while praying for more to come, a succession of UUP Assembly Members left Castle Buildings last night insisting that the joint proposal was "dead in the water." Contrary to the impression fostered by outsiders, they maintained that Mr Trimble had not attempted to sell the plan to them. And contrary to the widespread expectation in the press corps, Mr Trimble's most senior colleagues and aides told The Irish Times that he was not proposing to take it to a special meeting of the Ulster Unionist Council.
At a key moment in the negotiations on Thursday night it seems Mr Trimble did indeed make this offer to Mr Blair. If certain that actual IRA decommissioning would follow within a matter of weeks of the appointment of the executive, sources said Mr Trimble was prepared to seek limited flexibility to test that promise.
However, when all the one-to-one meetings had finally to come to an end, unionists (as many of them expected throughout) saw a yawning gap between the promise and the reality of the finished product. There was, in their view, no "certainty" of achievement, no republican "commitment" in terms unionists would understand, and, crucially no sanction to be applied exclusively to Sinn Fein in the event of non-compliance by the IRA.
Nor, let it be clear, was this only the Ulster Unionist interpretation. A succession of Sinn Fein spokesmen and spinners warned anyone who wanted to listen to what was actually being said was something less than an iron-cast guarantee of guns to be given up.
A plainly torn Trimble finally resolved his dilemma, taking a number of senior colleagues with him to tell Mr Blair his deal was neither believed nor acceptable. Some of those same colleagues, it now seems, resolved Mr Trimble's further dilemma - warning him, in the bluntest terms, that any attempt to take the proposal to the ruling UUC would fatally split his party.
If that position holds, it will spell a bitter disappointment for Mr Blair and Mr Ahern. But among their many calculations in the coming days, they will presumably want to consider what options will befall them should David Trimble suffer the fate of Brian Faulkner. Given the mood displayed by his party this week, that no longer seems unthinkable.