Hillary Clinton will travel to Northern Ireland on Friday for one of her last foreign trips as US secretary of state, lending support to a fragile peace that was one of the greatest successes of her husband's presidency.
Her visit comes as four men were arrested after a bomb was found in Derry. Police said the viable device was discovered after officers investigating dissident republican activity stopped a car in the Creggan area.
Tensions have been high in recent days after a controversial vote on flying the union flag over Belfast city hall.
Loyalists have been staging protests across the country to show their opposition to the decision to restrict the number of days the flag is flown.
Councillors from the non-sectarian Alliance party have been intimidated and in one case party offices in Carrickfergus, County Antrim were destroyed by fire.
The province has suffered one of the world's worst property market crashes and its leaders are hoping for US foreign investment.
"Our need is more economic now than political," said Reg Empey, the chairman of the Ulster Unionist party, who was a senior figure in the peace process.
"But we also have to be aware that there is still a degree of volatility ... and in those circumstances I think we should make sure we keep the relationship going."
Clinton travelled to Northern Ireland several times in the mid-1990s while her husband helped broker the 1998 Good Friday peace accord, his hands-on approach widely recognised as crucial at moments when the agreement looked like crumbling.
Bill Clinton's work helped win over the Irish vote during his re-election campaign in 1996 and his popularity among Irish Americans could rub off on Hillary should she decide to run for office in 2016.
"I'm not making the assumption that Hillary's career as a frontline politician has ended," Empey said. "If you have someone in the White House with good working knowledge of the north and the peace process, that can only be good for us."
Clinton on Thursday told journalists in Dublin she was "too focused on what I'm doing" to think about a run for the presidency.
She declined to comment on US newspaper reports that her husband may be appointed as Washington's next ambassador to the Republic of Ireland.
As first lady, Clinton lent support to pro-peace women's groups in Northern Ireland and visited people injured in the 1998 Omagh bombing, the deadliest attack in the Troubles.
"The lessons learned here in Ireland about how to build peace could be of great use to other peoples and nations," Clinton said in a speech in Dublin on Thursday in which she recalled a meeting between Catholic and Protestant women in Belfast in the 1990s, with one of whom she remains friends.
"There are so many more ties that bind us than divide us, and that is what has motivated me over many years now," she said.
The 1998 peace has mostly held, although militant nationalists have stepped up attacks in recent years, shooting dead a prison officer on his way to work last month.
Riots have broken out twice this week after nationalist councillors voted to take down the union flag on top of Belfast city hall.
"The people who are managing the low level [of violence] at the moment could make a mistake and suddenly we would have an awful lot of trouble," said Malachi O'Doherty, a writer and veteran political commentator.
"We don't really need American help, other than investment … That's where they will be dropping the big hints."
Clinton will also hold talks on a Northern Ireland economy reeling after house prices fell by more than 50% since 2007. The Troubles led to decades of under-investment and the province remains heavily dependent on a grant from London.
Financial services group Citigroup in 2010 announced the creation of 500 jobs in Northern Ireland weeks after Clinton held an investment conference for the province in Washington, but US investment remains a tiny fraction of that in the Republic of Ireland.
In Derry on Thursday night, a number of homes had to be evacuated as army bomb disposal experts made safe the bomb, described as a viable improvised explosive device.
SDLP Foyle MLA Pat Ramsey said people in Derry were angry at the disruption caused by the bomb. Two men aged 47 and 49 were arrested at the scene at about 8.40pm. Two others, also in their 40s, were arrested later.
A spokeswoman for the Police Service of Northern Ireland (PSNL) said: "All four have been taken to Antrim Serious Crime Suite and are assisting police with their inquiries."
Ramsey said: "Once again the people of Creggan are the victims of disruption, distress and anger. There is a palpable sense of anger – and relief that nobody was hurt. It could have been much worse."