There's a theory abroad at the moment that if the Belfast Agreement capsizes republicans will be able to salvage the pieces they like while David Trimble and the Ulster Unionist Party will be in pieces.

According to the theory, if the agreement falls, those elements of the accord favourable to republicanism, such as the North-South bodies, the North-South Council, the Patten report on policing, the criminal justice review, the human rights and equality agenda will be implemented.

Moreover, within the broad nationalist community, unionists will be blamed for the demise of the Good Friday accord, with the result that there'll be more sympathy for Sinn Fein, which consequently will eclipse the SDLP as the main nationalist party.

Meanwhile, what is most dear to unionists - Stormont Mark II - will be scrapped. Thereafter, bye-bye David. And good riddance, as far as Messrs Adams and McGuinness are concerned.

The idea is that what's happening at Stormont is part of a republican plot to split unionism further, to nudge the SDLP aside, and to reap the benefits of the Belfast Agreement still. Some unionists suspect that the weekend get-together of Sinn Fein in Co Donegal was designed to fine-tune further that labyrinthine plan.

Unionists don't trust republicans. If there were even a measure of trust, David Trimble probably would have been able to test whether the so-called seismic shift of July was in effect an IRA commitment to disarm.

At the time Mr Trimble couldn't buy the argument that it was a win-win gamble: that if he formed the executive and the IRA didn't deliver then Sinn Fein would be ostracised; or, if he formed the executive and the IRA delivered, then the Yes side had won.

There's speculation that the UUP's seminar in Scotland was designed to test whether the Assembly grouping could run with some variation of that formula: possibly going into government with Sinn Fein, but if the IRA did not start disarming within a set period - a month or six weeks - then the UUP would pull the plug on the Assembly.

Such a proposal could create possibilities around the idea of sequencing. But the trouble here is that republicans are also mistrustful of unionists, and seem genuinely perplexed by Mr Trimble. They feel, having been spurned once, that the First Minister must do more than flutter his eyes to persuade them they again won't be left standing under Clery's clock, so to speak.

Senator George Mitchell is here to do business. If he can't, he will pack his bags. He knows that if the next few weeks of negotiation are to have any chance of success, republicans must at least return to their "Way Forward" position.

Last week, republicans were sending mixed signals about their intentions, but Sean Crowe, Sinn Fein's Dublin candidate in the European election, was confident enough to state: "The proposal is there if the parties want it back on the table."

At some stage the realisation must be getting through to Gerry Adams and David Trimble that they are mutually dependent on each other. Mr Adams must surely realise that Mr Trimble's insistence on a republican move on decommissioning is not just tactical gamesmanship to see who'll blink first.

Equally, the UUP leader must be aware that while Mr Adams's leadership position appears sounder than his own, there are rumblings of discontent within the provisional republican constituency as well, not to mention the growing threat from the "Real IRA" and the other dissidents.

"There is no Machiavellian plot," Sinn Fein insists with considerable justification. "Adams and McGuinness have invested about 10 years of their careers in this enterprise. They've led from the front and persuaded republicans to take risks that a few years ago would almost have been inconceivable. If the agreement goes down, their leadership will have been weakened."

Despite the gloom and the atmosphere of desperation, despite the word from many British and Irish politicians that the Belfast Agreement is a hopeless cause, there is still a 50-50 chance of the agreement being saved. That will depend on Mr Adams and Mr Trimble taking more risks.

They might not be able to do that on the basis of trust, but could self-interest be a motivator?