Following Mr David Trimble's victory at the Ulster Unionist Council meeting, it is difficult to see how (even if he were of a mind to) Mr Jeffrey Donaldson can avoid carrying through with his threat to leave the party, writes David Adams.
For him to renege now on his very public, albeit thinly disguised, declaration that he would quit if defeated, would probably be more than his political credibility could take. One can readily imagine some of the less-than-flattering references to Clare Short his political opponents will have rehearsed just in case he does change his mind.
There is, I suppose, an outside chance of him reverting to that perpetual get-out clause much beloved by politicians - "I have been inundated with calls from distraught constituents" - but I doubt it.
All bridges seem already to have been burned.
So the focus of attention now shifts to when Mr Donaldson will go, where he will go to and, probably most critical, how many like-minded Ulster Unionists he might take with him.
He had initially indicated that his final decision would be made public later this month after a no-confidence motion laid against him by 70 members of his Lagan Valley constituency association had been dealt with.
Even though his local detractors have now decided, "in the interests of party unity," to abandon their motion, that timetable may still apply.
For rumour has it that Mr Donaldson himself will insist on a vote still being taken.
If he does, he might live to regret it, for it is by no means certain he would carry the day.
If he forces a vote before he has finally made clear his intentions, Mr Donaldson's constituency colleagues would find themselves in the invidious position of being asked to express support for someone who has given every indication that he is about to leave their party. And, irrespective of what side of the pro- or anti-Agreement argument they happen to be on, for the vast majority of Ulster Unionist members in Lagan Valley, the party always comes first.
A ringing endorsement from local activists will be even less likely if rumours persist that Mr Donaldson intends joining Mr Ian Paisley's Democratic Unionist Party.
To say that there is little love lost between the UUP and DUP in Lagan Valley is something of an understatement.
Some years back, the DUP publicly questioned the personal courage of Mr (now Lord) Jim Molyneaux, a second World War veteran, one-time party leader and, at that time, the highly respected Ulster Unionist MP for Lagan Valley. Those comments have never been forgotten, or forgiven, by many in the constituency.
So, all things considered, it is quite possible that Jeffrey Donaldson could bring upon himself another embarrassing defeat, only this time at the hands of his own constituency association.
When he does leave the UUP, it does not necessarily follow Mr Donaldson will consider the DUP to be his natural political home. The differences between them are actually more pronounced than it would sometimes appear. Mr Donaldson's position is probably best characterised as being about halfway between the polar opposites of pro-Agreement unionism and the DUP. Though, doubtless from his perspective, it must feel more like being caught somewhere between a rock and a hard place.
While he seems to favour adjustments to the Agreement, albeit some quite fundamental ones, the DUP are in the business of destroying the Agreement and starting afresh.
And, whereas the DUP have made it a point of principle not to enter into direct negotiations with Sinn Féin, Mr Donaldson has, as recently as last week, publicly stated that he would have no difficulty in "taking on Sinn Féin" in negotiations.
Besides, how comfortable would he actually be in a party that doesn't tolerate for an instant any straying from the party line by its members?
Despite public protestations to the contrary, it's a safe bet that many of his colleagues in the UUP will be glad to see the back of Jeffrey Donaldson. Initial concerns were centred on whether or not he would take a substantial number of people with him. Those fears have proved groundless. None of the big hitters within the party have shown any inclination at all to follow Jeffrey to the exit door.
Perversely, the leadership must now be worried that not enough of the lesser lights amongst the anti-Agreement faction will follow his lead and further ease tensions within the party.
For his part, it seems clear that Jeffrey Donaldson has little alternative, for the time being at least, but to sit in splendid isolation at Westminster as an independent unionist MP.
While David Trimble and his colleagues are that little bit freer to concentrate on the battles that unionism should have been concerning itself with all along.