On a human level, the tragedy of the Taoiseach's Mahon tribunal performance is almost Shakespearean. Nobody has enjoyed reading the nonsensical, rambling, shambolic replies he has given every time the forensic questioning of tribunal barrister Des O'Neill put him on the spot. Even worse has been watching or listening to the RTE reconstructions.

The multiple changes in explanations, as he lamely tried to counter the tribunal's exposure of his initial story that the money was to pay for legal fees arising from his separation, have strained his credibility to breaking point.

The tragedy is all the greater because, as leader of this country, Ahern has been the man whose charismatic ability to push friends to the limits of their ability and persuade enemies to breach the limits of their intransigence is the stuff of political legend. Yet he is diminished, and diminished by his own actions and his own words.

Every political action Ahern has taken recently, whether in Paris for the opening of the Irish College, at the rugby match, back at the Mahon tribunal, on the first day of the Dail, at the National Ploughing Championships for goodness sake, was dominated by questions about or references to the wads of cash that kept appearing on his desk. Everything he does now carries with it the mental picture of briefcases and safes bulging with cash as well as very strange methods of buying a house.

Bertie Ahern is, despite his achievements, despite the historic third term he so recently won, a lame-duck Taoiseach.

But if this were not bad enough, his behaviour now is degrading politics and public service.

This is not because, as Ahern sees it, younger members of Fine Gael have overstepped the mark by questioning his veracity, but because his government cannot survive unless its members collectively endorse the conflicting answers and amnesia the Taoiseach must dredge up to explain the unacceptable . . . his acceptance of a large amount of cash when he was a serving minister for finance.

He is asking fellow Fianna Fail ministers and TDs to diminish themselves. How many now have trotted out the line that they would not personally take money in this way but that Ahern's difficult personal circumstances in some way exonerate him from any taint? Brian Cowen, Mary Hanafin, Micheal Martin, Dermot Ahern, Noel Dempsey, Seamus Brennan and Willie O'Dea, to name but the most visible, have all squirmed as they have tried to square the circle of it being acceptable for their leader to take cash which they wouldn't touch themselves.

Loyalty, as we have seen before in Fianna Fail, comes before political principle.

Now, however, both the PDs and the Greens are involved in this debasement of our political system. It is true that they knew about the money before they signed up for government, making a pact that, as they rationalised it, put pragmatism above pure principle in order that they could pursue their visions for health and the environment. But the abysmal answers given by the Taoiseach are putting that decision to a real test.

The Taoiseach is scheduled for three more Mahon tribunal appearances over the next year. Will the Greens and Mary Harney hear no evil, speak no evil and see no evil as the circumstances of the Taoiseach's house purchase and the Manchester gifts are probed? To go on like this is simply not sustainable.

Many have criticised Fine Gael leader Enda Kenny and Labour's Eamon Gilmore for their rush to bring a motion of no confidence in Bertie Ahern on the first day of the Dail, but it has had one effect. It has exposed the extent to which both coalition partners, for all their bluster about standards in politics, have been compromised.

With no party in government now able to give a straight answer to a straight question, this entire affair is undermining our political process.