History shows us that even the greatest politicians suffer defeats and often - to borrow Enoch Powell's line - see their political careers end in failure.

Eamon de Valera dominated political life in the first 40 years of the new state and spent two decades in the top job, but he also lost two general elections.

Jack Lynch was famously described as the most popular politician since Daniel O'Connell and won elections in 1969 and 1977 (the latter an astounding 20-seat majority).

But, in between, he had to play second fiddle to Liam Cosgrave's Fine Gael/Labour coalition, which snatched power away from him in 1973. Lynch's final years as Fianna Fáil leader and taoiseach were marked by dissent and divisions that, arguably, drove him out of the leadership.

Seán Lemass, widely regarded as our best-ever taoiseach, never lost an election, but neither did he ever win an overall majority at a time when that was expected of Fianna Fáil leaders. Charles Haughey and Garret FitzGerald, meanwhile, both lost as many elections as they won.

Albert Reynolds endured a disastrous general election in 1992 and the resulting coalition government with Labour collapsed a couple of years later, prompting him to resign as Fianna Fáil leader.

But, based on last week's Sunday Tribune Millward Brown/IMS opinion poll, Bertie Ahern is firmly on course to remain untouched by failure. At 44%, Fianna Fáil and the PDs are a point ahead of their 1997 performance when they were able to put together a minority government. And, as things stand, it's difficult not to see Ahern returning as taoiseach, which, given his commitment to bow out at age 60, would leave him with an unblemished record.

Undoubtedly, luck has played a part in that success.

Ahern had the good fortune to be leader of Fianna Fáil at a time when coalition government was a realistic option - de Valera, Lemass, Lynch and Haughey (until 1989 when he finally dispensed with Fianna Fáil's core value) never had that luxury. He has also been leader during the greatest economic boom in the history of the state.

While it would be churlish not to acknowledge his role in maintaining the good times, one has to wonder whether Ahern's 'consensus at all costs' approach would have worked in more difficult times. Would he, for example, have been willing to face down opposition and administer the tough medicine delivered by Charlie Haughey and Ray MacSharry 20 years ago that led to the first stirrings of the Celtic Tiger?

But what is not in doubt is Ahern's political acumen. As a political strategist - concerned with the business of winning elections and staying in power - the taoiseach simply has no peers. When he took over as leader of Fianna Fáil at the end of 1994, the party looked to be in terminal decline. It would probably have plummeted below 60 seats if a general election had been held then, as public opinion held the party responsible for the breakdown of the FF/Labour government. Yet, within two-and-a-half years, Ahern was taoiseach after an election that he had no right to win.

In reality, the 'Bertie' phenomenon, not Fianna Fáil, won that general election.

The Rainbow government had performed well between 1995 and 1997; John Bruton, it was widely acknowledged, had been a good taoiseach. But, ultimately, this proved less important than Bertie Ahern's personal appeal.

And despite a decade in government, there is little sign of that waning. Much has been made of Enda Kenny's performance at the height of the Bertiegate affair last autumn - that it was a point of no return for the Fine Gael leader. Comparisons have been made with the performances of Dick Spring and Mary Harney in opposition to Charlie Haughey in the early 1990s.

But pummelling Haughey - a hugely divisive politician whose time had clearly passed - is completely different to taking on Bertie Ahern, who is still seen with enormous affection by many voters. Kenny and Pat Rabbitte were faced with a serious dilemma when the story broke, because it was widely perceived that it involved deeply personal issues. In these circumstances, attacking the most popular politician of the past three decades carried an enormous risk.

With the benefit of hindsight, it does seem like the opposition got caught in noman's land. But who can say with certainty that if Kenny and Rabbitte had gone bald-headed for Ahern - particularly after that highly emotive, 'from the heart' Six-One News interview - that there wouldn't have been an enormous backlash against the opposition parties? It is also likely that the main opposition parties' response to Bertiegate was influenced by focus-group research and that they knew that excoriating Ahern - however justified it might seem to be - would not play well with the public.

The problem for the opposition is that, with Bertie, the normal rules don't apply - dealing with him is akin to catching mercury with a fork. His single-minded obsession with politics is without parallel, and tactically (the man described by Haughey as "the most cunning"), he always seems to be two steps ahead of his merelymortal rivals. The reasons for this popularity are not easy to pinpoint - managing to be all things to all people is certainly one of them - but the enduring nature of that popularity cannot be disputed.

So, is Ahern unbeatable? The unpalatable answer for the opposition parties, facing yet another five year spell on the opposition benches, is that he just might be.