The moment of truth came came one Friday last month when Eileen Paisley addressed the DUP party executive when it gathered in Castlereagh Council offices, the same building where year earlier the same executive had taken the momentous decision to go into government with Sinn Féin.
The DUP leader's wife had provided crucial support for that move and when she spoke there was a respectful hush in the room. Or was it an embarrassed silence?
She wanted MPs present to issue a statement calling for her husband Ian to continue as leader of the DUP for the life of the assembly. She appealed to personal loyalty, reminding them of the debt they owed to the man who had started many of them on successful political careers.
The plea was met with silence. People shuffled their feet and their papers as the meeting moved briskly on to the next item. No statement was issued and it was left to Eileen herself to say, in an interview with the Belfast Telegraph some days later, that Ian had done "a jolly good job" and should remain. Nobody paid much attention, the writing was already on the wall.
It was the moment when the power of the Paisley family, which wanted Ian in power after so many years heckling on the margins, was finally trumped by the political organisation he had built around him.
It took some time for things to be arranged, and the rapprochement is already under way. Saturday a week ago Ian Paisley, Eileen and their son Ian (IPJ) were presiding over the annual dinner of Bannside DUP association, a roast beef and orange juice affair at Carnlea Orange Hall near Ballymena.
"He and Eileen were in good form. Doc was cracking jokes and had a word for everyone. There was no hint of what was to come on Tuesday. It took us all by surprise" a party activist said.
Had something happened over the weekend? A heave perhaps?
"He was pushed", says Jim Allister, a Euro MP who left the DUP to form Traditional Unionist Voice, the break away anti power sharing group which ate into the party's support in a council by election in Dromore last month.
"I am told that there was a document, my belief is that there were names on paper" said Allister. He believes that canvassing of DUP MLAs over the weekend had secured the support of the vast majority of them. It asked for Paisley to give a time table for his departure.
This account was supported by a number of DUP members early in the week but as soon as Paisley had made his announcement on Tuesday all 36 MLA's received e-mails from the party press office forbidding them to go beyond the approved line that Paisley was his own man, he had made up his own mind and nobody had pressured him. He was, as his deputy Peter Robinson had said in an approved statement, "a colossus of unionism". End of.
Despite the DUP's determination to make the transition of leadership as smooth as possible and to avoid any controversy, the idea that a straw poll was conducted is hard to doubt, particularly in view of the panicked reaction of the DUP press office.
"As soon as it became evident that he was looking at the issue [of retirement] there was a lot of talk about what the best time would be. Clearly the party talks about all these issues relating to the Doc but there was no petition and he was never handed any ultimatum" said Robinson, who had been discussing retirement issues with Paisley for several weeks, friends say since January.
"He spoke to me about it a number of weeks ago and the date I suggested to him was much longer than the one he has chosen" said Robinson who reputedly wanted Paisley to stay on until closer to the party conference in November.
"I can't tell you all the factors that were in Ian's mind at each particular time. All I can tell you is that the factors he stressed to me were that he needed a pause in the run up to September that allowed a new leader the summer to bed in." Paisley mentioned the anniversary of power sharing in May and a major US economic conference in Belfast on May 18th as events he wanted to preside at.
Robinson won't say when Paisley mentioned May as an appropriate moment to step down. Other DUP sources suggest that it was floated in mid January and that others, including IPJ, were in on the secret.
A whole nexus of events happened around that time. The first dent in his armour came when the Free Presbyterian Church, which Paisley had founded in the 60s and led ever since, removed him as moderator after complaints about his position in government with Sinn Féin. Then a front page article appeared in the Irish Times predicting that Paisley could go as early as the summer.
Paisley himself said he knew he could not remain in power indefinitely and IPJ told the BBC that Robinson should be the next DUP leader because of his loyalty to Paisley Senior.
The combined effect of the press leaks and IPJ's interview was to make it very hard for Paisley to back down from the leaving date. If he had been hoping that his friends would prevail on him to stay he was disappointed but Robinson says he was settled in his mind in any case.
"He had considered staying on until the end of the term, but he is 82 years of age he said and this seemed to be the right time to do it and the more he thought about it, the more it seemed right to him."
Paisley had already persuaded Downing Street to grant his wife a peerage. One of his main remaining considerations seems to have been to secure the political future of his son Ian who largely depended on his patronage for advancement. IPJ worked for Paisley as junior minister, as well as being his parliamentary researcher in Westminster. Paisley, who was never much of a man for the fine print of life, depended heavily on IPJ to handle the details of policy and correspondence for him.
"In the end it seemed as if Doc would have signed almost anything that Junior put in front of him" said a party source. However, he was forced to accept IPJs resignation after a series of financial allegations involving parliamentary allowances, office rents and the Paisley family's relationship with Seymour Sweeney, a property developer.
Just before last weekend Paisley appointed IPJ to the policing board, a move which his successor will be legally powerless to reverse This last act of patronage infuriated party MLA. They were also irritated by Gerry Adams using his Sinn Féin Ard Fheis speech to praise Paisley and call for him to stay on.
At the Ard Fheis, Ken Reid, UTV's political correspondent, started getting hints of what was coming and asked for an interview with Paisley the next week. However, by Monday morning things were still not clear; at a DUP officers meeting at 9.00 am Paisley gave no hint of his intentions.
"A number of colleagues later asked me why Ian did not call the party together and tell them what he was intending to do" said Robinson.
The final push factor may well have been the opinion of the DUP MLAs, which was conveyed to Ian Paisley Junior by Edwin Poots, the Culture Minister and one of Paisley's strongest personal allies. Ken Reid, who got Paisley's resignation interview as an exclusive on Tuesday, also heard about a signed document calling on Paisley to go.
"On Monday evening I was aware that they were getting together and that they had as many as 33 ready to sign and give it to Paisley, but it never came to that."
However, Reid denied claims by other journalists that he passed on the news to Paisley.
"I went in to see Ian Paisley before the interview on Tuesday and I asked him when he had decided to go. He said two weeks ago. During the interview he seemed relaxed and I got the impression he was enjoying it. He didn't seem pressured or hassled."
Robinson refuses to count his chickens before they are hatched but, barring some major upset, he will be the next DUP leader with Nigel Dodds, the Economy Minister, as his deputy. There is talk of a Blair/Brown or Reynolds/Ahern type arrangement in which Robinson, 59, will one day move aside for Dodds who is ten years his junior.
One thing that is likely to change under a Robinson leadership is the "Chuckle Brothers" bonhomie that existed between Paisley and McGuinness and which so unsettled the grass roots of both the DUP and Sinn Féin but delighted the media.
"I don't think anyone will want to do anything that will trivialise the campaign of murder in which the republican movement has been engaged" said Robinson.
"This is not our favourite process. Sinn Féin certainly is not our favourite partner. We are there because it was the best option available at this time for the unionist community. We resolved to do business on behalf of that community; we shall approach it in a professional and businesslike way."
The DUP also intend to make Paisley's last few months in office one long victory roll. They don't want things to close on a sour note. He will meet the Queen in Armagh next month, he will preside over the US investment conference with British and Irish Ministers, he will be showered with honours and all the manoeuvring of the last few weeks will be forgotten.
"Colossus of Unionism, that's the line" as the DUP press office put it.