Red-faced and with chest swelled in triumph, he was barely able to contain his delight, writes David Adams.
In the Assembly elections, the Democratic Unionist Party (DUP) had just out-polled the Ulster Unionist Party (UUP) to become the dominant voice of unionism.
Perched atop a mountain of votes, like a bantam rooster heralding the new dawn, he crowed for all he was worth.
He gleefully pointed to his own poll-topping, ego-boosting performance as evidence of the electorate's support for his persistent undermining of David Trimble's leadership and his unswerving opposition to the Good Friday agreement.
Remarkably for an Ulster Unionist MP, Jeffrey Donaldson's reaction to the DUP's triumph made Ian Paisley and his colleagues seem almost subdued in comparison.
For their part, the actual victors exercised a surprising degree of self-restraint, affecting an air of philosophic gravitas in contrast to their more characteristic bombast.
Perhaps, like the proverbial car-chasing dog, after capturing a prize that had eluded them for so long and been the object of such single-minded pursuit, they weren't quite sure what to do next.
Jeffrey Donaldson displayed no such hesitancy.
Within minutes of it becoming clear that Paisley's party had indeed won the battle within unionism, he was on television denouncing Trimble and calling for his removal as party leader.
Almost bursting with pompous self-vindication, Jeffrey pointedly refused to express any regret that the DUP had overtaken his own party in the polls despite repeatedly being invited to do so by a television interviewer.
He chose to ignore the 1.5 per cent increase in the UUP's overall share of the vote; Trimble's topping of the poll in his own Upper Bann constituency; and the part that he and a small band of likeminded UUP malcontents had played in ensuring the DUP's success.
When an arithmetically irrefutable point was raised - that an extra UUP candidate might just have been elected in his constituency if Donaldson and his election team had concentrated a little less on ego-boosting and a little more on vote management - it was angrily dismissed as nonsense.
Where four UUP candidates might have been returned, only a further two finally crawled over the finishing line to join Donaldson at Stormont.
The impression was that, if necessity had dictated it, his fellow candidates were to be little more than sacrificial lambs on the altar of Jeffrey's ambition.
How has the man who was once seen as the future leader of liberal unionism managed to confound so many people's expectations?
That Donaldson has an inflated ego and is driven by personal ambition is beyond doubt. But then, those traits are now taken as de rigueur amongst successful politicians.
The nature of the people from whom he takes political advice offers a better guide to why he adopts the positions he does and better explains his persistent hounding of David Trimble.
For the most part his advisers are old but, more than that, they are all old-unionist.
Chief among this group, and openly acknowledged as his political mentor, is the man from whom he inherited his Lagan Valley Westminster seat and, tellingly, from whom David Trimble inherited the UUP leadership, Jim (now Lord) Molyneaux.
Given the cumulative effect of his more recent behind-the-scenes manoeuvrings, almost perversely Molyneaux's decades-long leadership of the UUP was notable for little more than his ability to find consensus among the diverse strands of his party.
This he achieved by a combination of self-effacing affability and a refusal to countenance any political initiative, irrespective of whether it came from inside or outside the party.
During Molyneaux's tenure, the Ulster Unionists stayed united because he ensured they had little or nothing to fall out about. Where he was concerned, inactivity guaranteed unanimity.
Two public utterances give us further insight into Molyneaux's line of thinking: his now infamous declaration in 1994 that an extended IRA ceasefire would potentially be the most destabilising thing that unionism had ever had to face; and, more recently, his admission that he can't abide Germans on account of his wartime experiences.
The former says much about his reluctance to move beyond the pre-1994 status quo, while the latter speaks volumes about his inability to draw a veil over the past.
Since taking over as leader of the UUP, David Trimble's natural inclinations have, on all counts, led him in completely opposite directions.
Consequently, in comparison to Lord Molyneaux's relationship with David Trimble, Edward Heath could claim to have given rock-like support to his successor, Margaret Thatcher.
In moving ever closer to the DUP, Donaldson runs a real risk of repeating the same mistake Molyneaux made when he agreed to an alliance between the two unionist parties in the wake of the Anglo-Irish Agreement of 1985.
As Molyneaux found then, and various individuals and minuscule anti-agreement parties discovered to their cost in last week's Assembly elections, the DUP first colonises and then consumes its allies.