President Bush arriving at RAF Aldergrove, Northern Ireland

If you are out to impress the people of Northern Ireland, then Bill Clinton is a tough act to follow.

President George W Bush has not shown the same consuming passion for the Northern Ireland peace process as his predecessor.

But his arrival days before the fifth anniversary of the Good Friday Agreement is sign aplenty that Washington's influence on the peace process remains strong, if not as personal as before.

America's role in Northern Ireland changed dramatically with the election of Bill Clinton in 1992.

Bill Clinton: Three official visits

Within domestic American politics, the pull of Irish ancestry remains strong.

Some figures in Washington, such as Congressman Pete King and the Kennedy clan, have close ties to politicians in Belfast and Dublin.

Away from the public gaze, networks sympathetic to the republican cause were key to the Provisional IRA's arms supplies in the 1970s.

But historically, US presidents had tended to avoid Northern Ireland out of deference to their closest allies in Downing Street.

But that all changed with Bill Clinton. When he was on the campaign trail as the Democratic candidate for president in 1992, he promised Irish American voters he would send a peace envoy to Belfast.

The announcement infuriated London.

But by the time the peace talks reached fruition in 1998, Mr Clinton and his envoy, Senator George Mitchell, were pivotal figures in the process.

In from the cold

Mr Clinton's thinking was that he could bring republicans in from the cold by encouraging those within the movement apparently eager to completely replace the armalite with the ballot box.

Meeting: Historic handshake on Falls Road

One of his early and controversial decisions was to grant a visa to Sinn Fein president Gerry Adams in 1994. Again, London was hopping mad.

But, in hindsight, the visit enormously strengthened Washington's influence over republican leaders and reinforced the case for leaving violence behind.

By the time Mr Clinton arrived for this first official visit to Northern Ireland in November 1995, he had caught the imagination of the people.

Senator George Mitchell, who went on to chair the political talks, was of the same mould - seeking to be accepted as an honest broker.

The parties also realised that Senator Mitchell was not a token envoy but someone representing a president with a deep interest in events.

As the deadline for a deal drew near, Mr Clinton kept open a hotline to Stormont so that he could be called on to intervene in any last-minute disputes.

Without a doubt, he played a crucial role in the delivering of the Good Friday Agreement, and he remains recognised for this among Northern Ireland people.

Mr Clinton returned this affection by making Northern Ireland his final overseas trip before leaving office.

New administration

George W Bush came to power with a public determination to focus less on foreign affairs than his predecessor.

But at the first visit by Northern Ireland leaders to Washington for St Patrick's Day celebrations, the new president appointed State Department official Richard Haass as his special envoy.

NEW ENVOY We view paramilitaries and the sectarianism that allows them to thrive as the chief obstacle to normalisation US special envoy Richard Haass

President Clinton's policy had been to seek agreement rather than force one hand or the other.

The events of 11 September 2001 changed that. The Bush administration has had a far less tolerant view of the republican movement's links to violence than its predecessor.

At the heart of Washington's policy has been the IRA's suspected involvement in Colombia and its "war against terror" following 11 September.

Within a week of the Al Qaeda attacks on New York and Washington, Mr Haass warned republicans the suspected Colombia link could have "potentially serious consequences for the role of the United States in the peace process".

When devolution faced collapse in October 2002, Washington hardened its line.

Mr Haass attacked UUP leader David Trimble for setting a deadline for pulling out of power-sharing, accusing him of adding to a sense of crisis.

But he added: "We view paramilitaries and the sectarianism that allows them to thrive as the chief obstacle to normalisation."

Following the return of direct rule, Mr Haas reiterated Washington's belief that paramilitaries "must go out of business".

"The fact is that political institutions in Northern Ireland, like everywhere else, depend upon a foundation of trust," he said. "And simply, the requisite level of trust was no longer in existence."

What is clear is that the Bush administration agrees with Prime Minister Tony Blair that there needs to be "acts of completion" by paramilitary groups.

This, inevitably, has put the heat on Sinn Fein and heartened unionist leaders who have long considered Washington's policy as being influenced by a one-sided view of the conflict.