"You're a great man for the figures, " one shouted. "What about a whipround?" another interjected. The laughter and glee that arises from mischief-making followed. The Fianna Fail eyes were diverted downwards.

Bertie Ahern looked very vulnerable. And yet there was no mention of the Mahon tribunal as the opposition poked fun at the Taoiseach last Wednesday morning in the Dail chamber. The Health Service Executive was under discussion. Ahern rattled off statistics and figures in defence of the government's record. "Would you not organise a dig out?" yet another Fine Gael deputy asked.

The man who couldn't remember crucial details about his own personal finances was asking to be believed about health expenditure. Suddenly, it was hard to take the Fianna Fail leader seriously.

Political leaders need two qualities to survive in office . . . authority and credibility. Ahern has lost all credibility; the public don't believe him, or his "cock and bull" story, to borrow Eamon Gilmore's phrase. Moreover, he has already ceded authority to Brian Cowen and what little he has left is ebbing away with each day he remains in office. Ned O'Keeffe is an unlikely stalking horse. One rebel hardly makes a heave but the actions of the Cork politican in missing the confidence motion vote is privately admired by many of his parliamentary party colleagues. And just what was under discussion in Limerick last weekend when Brian Cowen met Willie O'Dea for a few Saturday evening pints? Internal plots abound in private but the real politics will also not get any easier for Bertie Ahern. He faces difficult months ahead with a tough budget, continued uncertainty in the property market and a dysfunctional health service. Against this backdrop, several seasoned Fianna Failers admit tolerance of Ahern's ongoing tribunal appearances will lessen. Having signalled his retirement date, Ahern weakened his own position. His vulnerability to ridicule like that in the Dail chamber last week only further lessens his grip on his job.

The Taoiseach limps on but it is only a matter of time before his own party cannabalises him in an act of self-preservation. Six months, 12 months, two years . . . it doesn't matter now, Ahern is a lame-duck leader serving out his final days in office. And yet the opposition know that the payments affair is unlikely to influence many votes at the next general election. The Drumcondra man will be history then, irrespective of the deliberations of the Mahon tribunal. Politics is a funny business because, already, Enda Kenny and Eamon Gilmore know their real targets are elsewhere in Fianna Fail.