Mr Tony Blair's speech in Belfast last night was of critical importance and significance on two fundamental counts.
First, by virtue of the emerging political landscape in Northern Ireland which obliged him to make it, and, second, for the undeniable truth he imparted in the process of doing so.
In contrast to the events preceding Good Friday, there were no public calls this time for the British Prime Minister to fly to Belfast and place his personal authority behind attempts to save the peace process. But as we awaited his arrival at the King's Hall, the context was plainly understood. The unionist campaign for a decisive Yes vote in next Friday's referendum is in mounting trouble.
Mr David Trimble's inability to prepare his constituency in advance for an all-inclusive settlement has been taking a steady toll. Private and public polling points to unionists recoiling in increasing numbers from a deal which would see paramilitary prisoners released and Sinn Fein nominees in a new Northern Ireland government.
A measure of Mr Blair's alarm lay in his acknowledgement that, while some opponents of the agreement could never be reached by rational argument, others had conveyed their concerns "in passionate terms" demanding of a "full answer."
The Ulster Unionist leadership moved promptly to align itself with the Prime Minister and welcomed a speech it concluded promised "plain and direct legislation linking prisoner releases and office (in the new Northern executive) to a permanent end to violence and decommissioning".
Mr Blair, the UUP said, was "honouring the pledges" he made to Mr Trimble on Good Friday. But Mr Jeffrey Donaldson, the key member of the Trimble team who found Mr Blair's last-gasp assurances unconvincing then, last night refused to rush to judgment on a speech in which Mr Blair moved as far as he could, while keeping to the terms of the agreement, to spell out his expectation of the decommissioning mechanisms for which the parties have signed up.
Mr Donaldson clearly faces a huge difficulty. Better, he may reason now, to have declared against last month and got the pain over with. Instead, by opting for the role of "constructive opposition", he had invited a sustained period of prime ministerial attention designed to bring him back to the Trimble camp.
Consulting his close allies late into the night, the Lagan Valley MP faced a horrendous choice: to disappoint Mr Blair and reject his efforts, or face brutal rejection in turn by those colleagues who firmly expect him to recommend a No vote - possibly even later today.
The signs are that Mr Donaldson may delay his verdict, and seek further "clarification" of Mr Blair's proposed legislation.
But if he sticks to his declared position, that there must be actual and ongoing decommissioning by the IRA before Sinn Fein can enter the proposed executive, then the likelihood is that he is lost to Mr Trimble. The reality is that, as Mr Blair put it himself last night: "We (the British government) are not setting new preconditions or barriers."
Mr Blair has clearly stated his expectations. He shares with Mr Trimble a rigorous view as to the implications for the IRA of Sinn Fein's decision to accept the benefits of the agreement and a full place in the democratic world. He has spelt out tough tests which flow logically and inevitably from the decision to share in a new administration. He says these tests will "provide evidence upon which to base an overall judgment - a judgment which will necessarily become more rigorous over time".
But the time-scale set out in the agreement is two years. And while the two governments have not yet finalised arrangements for the coming-in-to-being of the new institutional arrangements in their "shadow" form, the operative assumption is that this will be soon after the completion of the assembly elections next month.
Mr Donaldson has acquired huge importance at this stage because he represents a type of unionist wanting to support an agreement but as yet unpersuaded. By definition his acceptance of Mr Blair's assurances would be a potentially important boost to Mr Trimble.
Conversely, and inescapably, rejection would give further impetus to the unionist No campaign. Whatever Mr Donaldson decides, Mr Trimble could yet feel compelled to make further adjustments to his own position.
Fearing that Mr Blair could not do enough to satisfy Mr Donaldson, one British source yesterday wondered gloomily if the consequence of that would be to force Mr Trimble to draw his own line in the sand.
And here's the truth laid bare by the latest manoeuvres: we thought an agreement had been concluded on Good Friday, but for the Ulster Unionists and Sinn Fein, the negotiation process continues.