Small incidents can be telling. During the referendum campaign, Mr Robert McCartney was addressing the media at a Belfast news conference when the mobile phone of his associate Mr Cedric Wilson began to ring. Mr McCartney instructed him to switch it off but, instead of doing so, Mr Wilson walked out of the room to take the call.
A minor occurrence, certainly, but an indication that all was not entirely rosy between the two, and an early signal that Mr Wilson was determined to be his own man.
Dissident members of the Ulster Unionist Party who would, in principle, accept much of what Mr McCartney has to say but who still believe the battle against the agreement is best fought within the ranks of the biggest unionist party, described yesterday's events as "very sad".
"It's not the end of the beginning, it's the beginning of the end for Bob," said UUP dissidents. "He should have chosen his friends with a bit more care."
Their argument was that if the UKUP had given greater weight to the "loyalty factor" when choosing their candidates for the Assembly elections, yesterday's setback would not have occurred. But, frankly, few people expected the UKUP to do so well at the polls, securing the highly respectable total of five seats.
Now five has become one. Mr McCartney has challenged the four dissidents to resign their seats and stand for election under the new party affiliation. Mr Wilson has already rejected this challenge and pointed out that members who resign their seats are automatically replaced from a list of substitutes.
Apart from an unfortunate encounter in Holywood, Co Down, where he dismissed a group of middle-class women - one of whom had Alliance Party associations - as a "rent-a-mob", Mr McCartney was the media star of the referendum campaign. His well-marshalled legal arguments probably proved more persuasive with middle-ground Protestant opinion than the more strident approach of other anti-agreement unionists. His argument that the four dissidents would not have been elected without his name in the subsequent Assembly poll is a strong one.
But that was then, this is now. Politics is a cruel trade, and while Mr McCartney has some right to feel aggrieved, whatever support he may have among the party grassroots, he is now an isolated figure in the Assembly.
Mr McCartney has frequently drawn parallels between himself and Winston Churchill: a voice in the wilderness crying out against the appeasers of violence and brute force who would nevertheless be vindicated in the end.
It looks as if his isolation will become more intense in the coming months. Within minutes of the new party being announced, speculation was growing as to how long Mr McCartney could retain his front-bench position in the Assembly, not to mention the accommodation and financial allowances available to his party as well as the entitlement to chairs and/or vice-chairs of committees allocated under the d'Hondt system of proportionality.
The new party may have its own difficulties. A similar formation, the United Unionist Assembly Party, was granted recognition in the Assembly even though its members had not campaigned under that label in the election. However, one of them had the foresight to sign the roll on the first day as a member of the UUAP, which helped facilitate subsequent recognition.
A spokesman for the Initial Presiding Officer, Lord Alderdice, said after yesterday's announcement, "We are taking legal advice on the implications." The new party is also consulting the lawyers. Mr McCartney appeared to be resigned yesterday that what he considered political expediency, rather than strict legal principle, would result in the loss of Assembly privileges.
The split has thrown some light on an earlier episode in the life of the UK Unionist Party, namely the resignation of Dr Conor Cruise O'Brien following publication of his hypothesis that unionists might be forced to make a "United Ireland" deal with the Republic to avoid coming under the thumb of Sinn Fein in the North.
Dr O'Brien said yesterday that Dr Roche, in particular, had told him "quite imperiously" that it was his duty to resign. "I hung up on him," Dr O'Brien said. However, he then decided to leave the party to avoid giving Mr McCartney's opponents an issue on which his leadership could be challenged.
The new party has set its face against an "exit strategy". It says the best way to fight the Belfast Agreement is by working with other anti-agreement unionists in the Assembly.
Last night, 12 constituency chairmen and party representatives expressed their "contempt" for the actions of their former colleagues, now regrouping as the NI Unionist Party. "We reiterate our total confidence in Robert McCartney QC MP and remain fully united around his positive leadership," they said in a statement.
There will probably be more of the same from both sides in the coming days and weeks. Meanwhile, pro-agreement elements in the Ulster Unionist Party are enjoying the travails of Mr McCartney, who has been a thorn in their side for so many years.
The decision by Mr Wilson and his friends to opt for the politics of participation rather than boycott could be seen as a victory of sorts for the process which led to the Belfast Agreement. But their statement pointed out that while they would not walk away from Stormont, they were prepared to bring down the Assembly from within if that was the price of keeping Sinn Fein out of government. But those in the best position to do that are dissidents in the Ulster Unionist ranks. In that sense yesterday's events, though entertaining and probably of some importance in the long run, are still, in the short term, something of a sideshow.