It was a glittering gala evening at the Kennedy Library in Boston last month as the Taoiseach, Mr Ahern, saluted Senator Edward Kennedy for his "major role in creating and sustaining the Northern Ireland peace process".

Senator Kennedy was also a "taoiseach", a "chieftain" of the Kennedy clan, with his political vision and wisdom, Mr Ahern told the 300 guests.

But another Fianna Fail taoiseach, Mr Jack Lynch, had once rebuked Senator Kennedy publicly in the Washington Post for his call for British troops to be withdrawn from Northern Ireland, as part of a move to a united Ireland.

"I don't think he understands the situation as fully as we do," Mr Lynch told the newspaper in March 1972. In the period following the introduction of internment in August 1971, Senator Kennedy was infuriating the British government and worrying the Irish Government with calls for the withdrawal of British troops, the suspension of Stormont, a period of direct rule and a peace settlement leading to a united Ireland.

He compared the British presence in the North with the US involvement in Vietnam and the American media seized on the analogy "Britain's Vietnam". The British prime minister, Mr Edward Heath, called it an "ignorant outburst" and Mr Brian Faulkner, the Northern prime minister, accused Senator Kennedy of "playing American politics with Ulster people's lives".

Senator Kennedy fought back in an open letter to the London Times, saying: "It is difficult to believe that my proposal would have generated so much fervour if Britain, one of the great symbols of freedom and democracy to us in America, did not have a guilty conscience over Ulster."

Irish-American republicans supporting the IRA and contributing to Noraid were delighted with Senator Kennedy taking on the British, but four years later they would denounce him as a "British lackey". Mr John Hume played a vital role in what Senator Kennedy later called a "moderating" of his views.

They met first in Bonn in November 1972, when Senator Kennedy sought out Mr Hume for a long discussion. They have been close friends since.

But Senator Kennedy demurs at the view that Mr Hume was his sole influence. The Senator told the historian, Andrew Wilson, author of Irish America and the Ulster Conflict 1968-1995 that "my more moderate tone was a reaction to Great Britain's more moderate policy towards Northern Ireland."

Thus, Senator Kennedy was a strong supporter of the Sunningdale power-sharing experiment and praised Mr Heath, and even suggested Mr Willie Whitelaw for the Nobel Prize.

Likewise, as IRA and loyalist violence increased after the breakdown of power-sharing, Senator Kennedy began to denounce Irish-American funding and support for the IRA. He has denied to Mr Wilson the claim by former IRA member, Ms Maria Maguire, that he was used by the Provisionals to obtain US visas for their fund-raisers. With fellow Senator Daniel Moynihan, Speaker Tip O'Neill and Governor Hugh Carey of New York, Senator Kennedy formed an influential group nicknamed the "Four Horsemen".

They played a vital role in the policy formulated by then Irish ambassador to the US, Mr Sean Donlon, of weaning away Irish-American support from militant groups like Noraid. Their St Patrick's Day statement in 1977 condemning the men of violence marked a watershed and helped lead up to President Jimmy Carter's pledge the following August that US economic aid would be available as soon as a peaceful settlement could be reached. There were reports then that Senator Kennedy would go to Belfast to launch a peace initiative, although five years earlier loyalists had told a fellow Congressman that they would kill him if he ever came there. In fact, Senator Kennedy has never visited the North until now, and security must have been a factor in this absence.

He has worked hard to show he is not just a "green" Irish-American in relation to Northern Ireland. He has promoted research into the important role played by the Scotch-Irish from Ulster in the founding of the United States, and frequently refers to the impressive number of presidents of Ulster Presbyterian stock.

In recent years he has encouraged unionist and loyalist politicians to come to Washington and is always ready to receive them. By the 1990s, Senator Kennedy would have been seen as a determined opponent of IRA violence and a strong supporter of initiatives aimed at reconciling the two communities in Northern Ireland, with future British withdrawal based on majority consent.

He spoke out for the Anglo-Irish Agreement, the Ireland Fund, the Downing Street Declaration and the Framework Document. He looked to Mr Hume for guidance before supporting the movement to grant Sinn Fein leader Mr Gerry Adams a visa to enter the USA before the IRA ceasefire was called. His support is important to President Clinton, for whom the Senator's clout on Capitol Hill is important in getting liberal legislation passed.

The breaking of the first IRA ceasefire was a huge disappointment for Senator Kennedy, who said he would not meet Mr Adams again until it was restored, but he was also critical of the British government for allowing 17 months to elapse without getting inclusive negotiations going.

He tried hard last March, in the run-up to the British general election, to persuade the IRA to renew the ceasefire so that Sinn Fein could be at the table when the peace talks were resumed in June. He was disappointed when his call was unheeded, but the new ceasefire was not too long delayed.

Now Senator Kennedy sees his role as exhorting Sinn Fein/IRA not to become discouraged by the slow pace of the negotiations or be tempted back to violence. But he also sends a coded message to the unionist side when he says: "We must also oppose those whose intransigence is cynically designed to make the process fail".

Back in 1972, a leading member of Fine Gael told the Chicago Tribune that Kennedy "is a bloody nuisance. I wish he would shut up".

Everyone has learned a lot since then.