But it can also be a source of frustration to British prime ministers; never more so than now when the biggest party in Northern Ireland has threatened to reject a course which Tony Blair is absolutely convinced is right. He has none of the political levers in Northern Ireland which his party's permanent presence in Scotland and Wales afford him.
It follows that if the Unionists reject the new decommissioning proposals, despite adjustments to meet some of their concerns, Mr Blair's options look painfully limited. All the more so since it is impossible not to sympathise with the Unionists' hostility to the idea of sitting in a new Northern Ireland government with Republican politicians who have merely promised that they "could" persuade the terrorists to yield up their weapons.
Having seen the prisons steadily emptied of IRA murderers and gunmen and having lived with a low but persistent level of IRA punishment beatings and worse, they are now obliged to welcome Sinn Fein as colleagues on the vague undertaking of men who resolutely cleave to the blatant fiction that the party's leadership - and that of the IRA - are separate entities.
For democrats there is something deeply repellent about the idea of - say - Martin McGuinness exercising even for a matter of weeks a ministerial authority gruesomely enhanced by the shadowy presence of a still intact and well equipped private army.
Nor - as Mr Blair has recognised - was it exactly optimal that the new agreement stipulates that an IRA failure to keep to the planned decommissioning timetable would simply result in the new executive being suspended. If natural justice were the criterion, the agreement between London and Dublin last week would merely say that Sinn Fein should be expelled from it. The unstated reason why it didn't do that, of course, is that John Hume, leader of the Nationalists SDLP had not been prepared to contemplate an executive excluding Sinn Fein.
Mr Blair has good answers to these questions. To the argument that Sinn Fein has done nothing but produce soft words and fancy formulae on the totemic issue of decommissioning, he points out that those words are to be tested under the agreement by deeds - and quickly.
Under the fail safe mechanism, the Republicans have only to fail to meet that timetable to see the whole process unravel - and with it the most significant advance that they have made under the agreement: active participation in the government of Northern Ireland.
And while seeking to meet the complaint that this is unfair, Mr Blair points out that he cannot, however he might wish to, compel the parties - which in effect means the SDLP - to continue sitting on an executive if it does not contain Sinn Fein. Instead, if Sinn Fein fails to decommission it would be up to the parties to decide how to proceed.
Seamus Mallon, the deputy leader of the SDLP, has said he would personally argue in such circumstances for a continued executive without Sinn Fein. But in any case, the worst, from the Unionists' point of view that would happen, is a return to the present status quo: direct British rule without devolution.
And in those circumstances it would be the Republicans and not the Unionists who would take the blame for aborting the process.
But if none of this works with the Unionists? Good arguments, and a few further concessions, may not be enough. If all the Prime Minister's persuasive powers fail with David Trimble's party, he will surely have run out of the strategies he desperately needs to kick-start devolution and a lasting political settlement.
Or will he? There is one further possibility - dauntingly high risk, but not wholly unfamiliar in Northern Ireland. Almost the only power Mr Blair has to bypass roadblocks erected by the two parties representing the Unionists' majority is to appeal over their heads to the voters in a referendum. The hazards of such a daring, almost Gaullist course, lie in the fact that defeat for the new agreement in a plebiscite would set back the peace process, perhaps indefinitely.
There is a danger that Ian Paisley's DUP and, worse, Trimble's UUP would boycott such a poll, even though to do so would show a lamentable lack of faith in the party's ability to persuade the voters of their case.
To have any meaning, a referendum would need a majority not just of the Northern Ireland population but of the Unionist segment of it and to achieve that might require Mr Trimble and others to detach themselves from the sceptics and campaign for the solution now sought by London and Dublin - which Mr Trimble has understandably shown little eagerness to do in the past few days.
These are all real problems with the referendum idea. Perhaps such a proposal will remain as dormant as it seems at present. And there will be strong voices raised - if Mr Blair cannot now persuade the Unionists - in favour of slowing down the process. There is no need for indecent haste, it will be said. Perhaps when the marching season is over, particularly if it can be kept as relatively peaceful as was the weekend's Orange march at Drumcree, some further way can be found of bridging the gap between Unionists and Republicans. After 30 years of violence we can all afford to wait a little longer.
But there is a counter case to these siren arguments, namely that the lessons of the past two years is that progress is only made when momentum is maintained. That has been Mr Blair's way. He is at his most eloquent when he is arguing, not only that Unionism will get the blame if the process falters now but, more potently still, that the gains the Unionists have made are too valuable to put at risk - the principle of majority consent to Northern Ireland's constitutional status; the devolved assembly they have so long sought, and now the "seismic change" of an apparent Republican intention to decommission arms.
He is already reaching beyond the politicians to a people he believes ache for a lasting peace. It is a safe bet that a referendum - the second in the year - has been at some point canvassed deep inside the British Government. Perhaps this is just the sort of idea all responsible governments consider before discarding it. But it is hard to believe that if all else fails, there is not a part of the Prime Minister that would relish putting his case in a sustained campaign directly to the Northern Ireland people.Reuse content