A few days after the latest Hillsborough proposals - including the IRA's statement pledging to put arms completely and verifiably beyond use - were made public, a senior Northern Ireland Office source told me, "We couldn't have done this without John Taylor. He was crucial in convincing David Trimble that he could carry it with the UUC." Mr Taylor's immediate response seemed to bear out this account. The deputy leader of the UUP was, if anything, rather more positive about the deal than David Trimble himself. He told journalists that there would still be hiccups, but that he believed these would be overcome and that the proposals "would be approved strongly" by the UUC.
Within hours, Mr Taylor was warning that the whole deal could "unscramble" over the RUC. Since then, the Scarlet Pimpernel of unionism has been both elusive and evasive. His latest intervention came yesterday, when he was quoted in the Belfast News Letter as saying: "I would hope that David and myself would be singing from the same hymn sheet . . . But, naturally, if we weren't, I would do the honourable thing and resign as deputy leader."
There is an understandable temptation to dismiss this as yet another example of unionism's most unpredictable maverick doing his own thing. The suggestion is that Mr Taylor is trying to play both sides, giving comfort to the anti-agreement clique, while reserving the option of supporting David Trimble if the tide seems to be flowing in favour of a Yes vote.
Does it matter what lies behind John Taylor's change of heart and his current equivocal stance? Yes, very definitely. David Trimble has come out fighting for the Hillsborough deal and it must be a cause for dismay to both governments, not to mention pro-agreement unionists, that Taylor has failed to endorse his stance.
There are other reasons for concern. Taylor has been around unionist politics for a very long time and has a keen sense of his own community. He has helped to steady Trimble when the Ulster Unionist leader has had to take difficult decisions in the past, not least during the negotiation of the Belfast Agreement. His support for moving forward now would carry weight with a significant number of delegates to next Saturday's meeting and probably ensure a decent majority for David Trimble. Without his support, the vote will be a close-run thing.
For all these reasons, it's worth considering why John Taylor's first response to the deal was so positive, and why he has drawn back since. Piecing together accounts of what happened at Hillsborough in the late hours of Friday, May 5th, it seems clear that the UUP negotiators believed there were proposals on the table which offered them some comfort on the RUC.
These did not go so far as retaining the name of the force. But one section of the Bill would contain a phrase describing the new service as "incorporating the Royal Ulster Constabulary." This, it was hoped, would be sufficient to avoid giving the impression that the RUC, and those families still grieving for fathers, brothers and sons who had been killed by the IRA, were being "humiliated" by the change of name. Sinn Fein balked at this, as did the Irish Government, which was why the phrase was dropped from the Bill placed before the House of Commons.
Speaking on the BBC on Sunday, David Trimble tried to explain why the name of the RUC was of such emotional significance to the unionist community. He said great efforts had been made to ensure that any move by the IRA on weapons would not be construed as the defeat of the republican movement. Now it seemed that nationalists, by demanding the complete removal of the RUC's name and symbols, "wish to inflict a defeat on the police force and, of course, unionists feel that they are going to be humiliated".
It is fear of humiliation, of the defeat of one community at the hands of the other, that the whole peace process is designed to overcome. The hard reality is that the problem of policing in Northern Ireland is not going to be solved in the coming weeks and months. Almost everybody agrees that there must be more Catholics in the new force/service. But that will happen only when there are political institutions to which both communities can give their allegiance. Even when this does happen, the likelihood is that Protestants will continue to refer to it as the RUC, while Catholics call it the police service.
But, in the short term, symbols and language do matter - to both communities. The task is to arrive at a compromise which, as far as possible, avoids inflicting hurt on either side. Bertie Ahern knows this, which is, presumably, why he met members of the Northern Ireland Police Federation and widows of RUC officers earlier this week. This was a typically sympathetic gesture on the part of the Taoiseach, but it may be that something more concrete is required from the Government of this State.
The unionist community is at a historic crossroads and, not surprisingly, many people are fearful. Those fears have crystallised around the RUC and the suspicion that all traces of its past record are to be swept away.
Both David Trimble and John Taylor know that this is an issue which - like decommissioning within the republican movement - touches a deep emotional nerve in the broad unionist community. The Ulster Unionist leader, to his great credit, has decided to campaign on the substance of the current proposals, in particular the importance of the IRA's statement. His deputy believes that, in order to secure victory for the Yes camp this weekend, some further reassurance is needed that this is not another defeat for unionists.
Bertie Ahern should be asking what can be done to bring John Taylor - and those who share his concerns - back on board.