He waited for the DUP leadership for so long and now it seems to be slipping away. For almost three decades, Peter Robinson played bridesmaid to the Rev Ian Paisley, but his hold on the reins of power is weakening after less than two years in the job.

Robinson won the party's head when he became leader in 2008 but he never had its heart. He was respected for his sharp mind, negotiating skills and strategising. Nobody ever expected him to be weakened so quickly. He stood over a dramatic fall in his party's vote in last June's European election. Last week's revelations about the Robinsons indicate that DUP support could crumble even more dramatically in the Westminster election, likely to be in May. DUP seats in Strangford, North Antrim, North Belfast and South Antrim could all be at risk, as could Robinson's East Belfast seat.

When Peter Robinson appeared before the cameras last Wednesday as the cuckolded husband – haggard and emotional, stumbling over his words – viewers will have felt sorry for him. But closer examination, and time, reveals a different picture. It was a carefully choreographed event. Four hand-picked journalists were taken to Robinson's home – a formal office setting would never have worked – where he read from a printed script. The public's heart-strings were skilfully pulled.

A plaque reading 'Dad, no matter how tall I grow I will always look up to you' sat prominently in the background. But as Robinson spoke so movingly about his wife's affair and attempted suicide, the question remained as to why he was emotional now.

Iris had confessed adultery and tried to kill herself 10 months earlier. Was Robinson devastated over Iris or was the real cause of his distress the fact the BBC's Spotlight programme had sent him a list of questions the previous day and Robinson knew his political career was hanging by a thread?

This cynical interpretation seemed validated when we later found out that, hours after he learned of Iris's affair and attempted suicide, Robinson was in the Assembly, cracking jokes and in fine form. It was Iris's political adviser, Selwyn Black, who was left to sit at home with her and liaise with medical carers.

Robinson's actions hardly fitted the image of a devoted husband he is now attempting to convey. Indeed, his response on 2 March 2009 to his wife's situation, regardless of her adultery, smacks of extreme coldness.

"Peter gave an Oscar-winning performance for the cameras on Wednesday," says one DUP member. "It was a damage limitation exercise and most of the press fell for it."

The obsequious media coverage meant Robinson won the sympathy vote until the revelations in Darragh McIntyre's masterly Spotlight programme the following night.

The announcement after Christmas that Iris was stepping down from politics due to "stress and strain" can also be viewed cynically. Despite her financial wrongdoings, adultery and attempted suicide, she had no such plans just a month earlier. No way would she be retiring from politics, she told the Newsletter in November: "I've so much still to do and so much want to be part of political life." So were Iris's newly announced retirement plans motivated by rumours of the Spotlight programme?

With a click of her fingers, Iris secured £50,000 for her lover's business from two builders – Ken Campbell and the now deceased Fred Fraser. To do this, she must have had a close working relationship with them. As Iris was securing the money from Campbell, she was lobbying for one of his building schemes.

The Robinsons' actions over the years in relation to planning applications by both developers must now be scrutinised. Fraser in particular was a major player on the Robinsons' home turf, the Castlereagh Council area. The law states that, once Iris had a financial interest in a business, she had to declare it. She didn't. When her husband discovered her financial dealings, he insisted the money be returned but he didn't tell the authorities what he knew. That is not what is expected of the holder of the North's highest political office.

Paul Berry was suspended by the DUP after a homosexual liaison in a hotel room. Iris's adultery and financial wrongdoing didn't prompt any such swift action. That smacks of double standards.

Minus the Robinsons, the DUP has seven MPs. Four – deputy leader Nigel Dodds, Jeffrey Donaldson, Sammy Wilson, and David Simpson (as well as Stormont minister Arlene Foster) – issued statements supporting Peter Robinson before the Spotlight programme was aired. The Sunday Tribune has been told they didn't know the full content of the programme at the time. If Robinson is increasingly seen as damaged goods, then those politicians, especially Dodds, who supported him so strongly will have to distance themselves from him.

Three MPs – Ian Paisley, Willie McCrea, and Gregory Campbell – didn't issue statements supporting Robinson. If Robinson does go, the talk is of a Dodds-Campbell ticket. Paddy Power makes Dodds 6/5 favourite to succeed Robinson. Campbell, regarded as a hardliner, would appease unionist grassroots increasingly unhappy with the DUP leadership's direction.

The party is at a crossroads. Iris is departing the stage and Peter could be delivering his final lines. The House of Robinson is teetering on the brink.