James Galway summed up David Trimble's achievement and the scale of the difficulties which still face the Ulster Unionist leader. The man with the golden flute was playing alongside Phil Coulter to an ecstatic crowd in Derry's Guildhall Square on Monday.

He told the audience that this was a great day for the whole island. "They managed to get David Trimble up and running. It was probably the first time that the whole Catholic population was praying for a Protestant."

Therein, of course, lies the rub. Trimble's victory at the Waterfront Hall was greeted with enthusiasm by almost every shade of green. The Belfast Agreement has always been more popular among nationalists, while support on the unionist side has steadily eroded.

The threat to Trimble's future comes from within his own community. This is no surprise. It has happened to other unionist leaders who tried to forge an accommodation with nationalism, but Trimble has always seemed better placed to avoid the fate of Brian Faulkner.

Now the storm clouds are gathering again. One of the first delegates to whom I spoke at the Waterfront Hall on Saturday, just as the vote was announced, was a Trimble supporter. He said grimly: "It looks as though we'll be back for the leadership heave by the autumn."

Another Yes voter, a retired police officer, told me he had supported Trimble with a heavy heart. He had little confidence that the IRA would deliver on its promise regarding arms, but saw no alternative to having another go at making the Executive work. He believed that Trimble had been an adroit leader and was prepared to trust him, for the moment at least. The No side is determined to wreck the agreement. The old IRA mantra, "we only have to get lucky once", was used several times on Saturday.

Peter Robinson is upbeat about his party's longer-term strategy, which is to form a bloc of unionists, including UUP dissidents, within the Assembly who will have the capacity to vote against every step of the implementation of the Belfast Agreement. The No side is a few votes short of the magic 30 needed to make up 60 per cent of the unionist representatives in the Assembly. However, two members of the UUP who declared against Trimble on Saturday could carry their opposition into Stormont.

At his press conference last Saturday, David Trimble spoke, in words which caused real and unnecessary offence, of the need to "housetrain" Sinn Fein. He well knows his first priority must be to put manners and a degree of parliamentary discipline on his own dissidents.

There has been talk of the need to "modernise" the party, which would involve reducing the power within the Ulster Unionist council of special interest groups like the Orange Order, exercising greater control of the selection of parliamentary candidates, and so on. This will not be enough to stop Jeffrey Donaldson and others even more vehemently opposed to the whole spirit of the Belfast Agreement.

It has always been a characteristic of Trimble's leadership that he prefers to try to reconcile the differences within his party, rather than confront them. Perhaps this has been due to a lack of confidence in his own strategy, but his inclination has been to invite his opponent back into the tent, a tactic he has tried several times with Donaldson. In many ways this emphasis on party democracy is an attractive trait, but if Trimble is to hold on to his own supporters, many of whom took political and personal risks last Saturday, he must show that he is not prepared to tolerate constant sniping at his leadership on every issue. That means taking a tough line with the dissidents.

This isn't going to be easy. There are a number of issues on the immediate political agenda which might have been designed to add to simmering resentments in the unionist community - the future of the RUC, the flying of the Union flag on public buildings, decisions on contentious Orange parade routes. Add the possibility of continuing loyalist violence, internecine or directed against vulnerable Catholics, and you have the makings of a potentially vicious brew leading up to Drumcree.

The threat of a full-scale challenge to Trimble's leadership will not go away and there is likely to be more talk of rebellion as constituencies select their candidates for a probable British general election next spring.

Last weekend the fate of the Belfast Agreement - and hopes for a political settlement in Northern Ireland - rested on the votes of just 56 delegates to the Ulster Unionist Council. Many of them still have serious worries about the whole project. Trimble has to show them that the new dispensation can work for the good of the whole community.

This is why James Galway's comments on the prayers and hopes of the Catholic community seem particularly relevant. The vast majority of nationalists support the agreement and believe that it can provide a new way forward.

They know there are still obstacles to be overcome and issues such as the Patten report which are a matter of serious concern, but they are proud to see nationalists and republican ministers in government and are rightly convinced that real gains have been made. They also recognise that David Trimble has played a courageous role in making this possible and have demonstrated a generosity which has sometimes been lacking in their political leaders.

If this project is to work there must be a more serious attempt to build a sense of shared responsibility between unionist and nationalist ministers. We are told that representatives from all the parties have worked well together at committee level but have yet to see this happening at the level of the Executive.

It would be a good start if Seamus Mallon and David Trimble could be seen to overcome their mutual prickly mistrust and work together in a new partnership for peace.

mholland@irish-times.ie