In historical, ideological and, even more importantly, emotional terms, the significance of Sinn Fein's biggest step towards supporting policing is difficult to underestimate.

Mainstream republicanism has put a century of trenchant - and violent - opposition to policing in Northern Ireland into reverse.

They have crossed a republican Rubicon. And there is no way back. Yet, it would be important also not to overstate the shift it represents.

For, at least in the short term, the Sinn Fein shift yesterday is tactical as well as strategic. Mainstream republicans facing the policing issue finally concluded: "Yes - but not yet."

Veteran party member and Belfast councillor Tom Hartley accurately described the decision as a fundamental change in Sinn Fein's strategic direction.

But yesterday was about much more than the hand of history. It was about the heart and the head, too; in fact, probably the entire upper body - leaving only the legs as there could be a kick or two yet on the road to devolution.

For the lengthy motion carried forward clearly defers activation. Support for policing has been agreed. But it will not be put into effect until the time is right.

The result of yesterday's long- anticipated ard fheis was never really in doubt - the only issue was the margin of the leadership's victory.

Gerry Adams, Gerry Kelly and others repeatedly insisted the verdict was not 'in the bag' precisely to put pressure on waverers to vote in their favour.

Had the motion been lost, not only would the peace process itself have been plunged into freefall, the present Sinn Fein leadership would have been in crisis as well.

But the republican leadership leaves little to chance. Thus, most of the party's local units across Ireland mandated their delegates how to vote. Others were given the freedom to decide how to vote on the day, but it was impossible to quantify their strength.

Only Ogra Sinn Fein, the youth wing, went public with its decision to vote against, but it had less than 20 votes to work with.

A mid-Ulster activist said party units in the north west had been allowed to make a final verdict yesterday.

And there were boos when, as the queue of speakers stretched further and further, it was suggested that speaking time be cut from three minutes to two.

Those who broke the three- minute deadline tended to be loudly cheered. While there were complaints that, as one delegate put it, "for some strange reason" amendments had been withdrawn, there was no attempt to curtail debate. But dissenters were outnumbered by about eight to one.

To a large degree, Sinn Fein could not deliver on the force of their motion even if they wanted to. The Policing Board - to which Sinn Fein can now allocate members - will not be reconstituted until after the Assembly elections of March 7. No delivery on that before the election, then.

Similarly with district policing partnerships. Both the motion and its proposer, Martin McGuinness, made clear it is for the PSNI "to make strenuous efforts" to earn the trust and confidence of nationalists and republicans. In his keynote speech of the day, he made little attempt to justify or explain Sinn Fein's strategy.

Instead, he touched all the buttons - the sacrifice of volunteers; the " hurting" of republican families; the ineffectiveness of republican dissidents and their collective enemies including 'securocrats' and unionist 'rejectionists' - designed to bring about his "decisive Irish republican yes".

But on the issue of trust between former sworn enemies who are expected to bury the past and work together to deliver policing, he insisted: " They're not going to get that trust tomorrow morning."

But, above all, the motion transfers the authority for implementing support for policing to the party's ard chomhairle (executive) at a time of its choosing. That will be, it says, "only when the power-sharing institutions are established" and when the executive is satisfied policing and justice powers will be transferred to the Assembly and Executive.

But if power-sharing is not returned by the St Andrews timetable of March 26, then implementation of support for policing will happen "only when acceptable new partnership arrangements to implement the Good Friday Agreement are in place".

If the ard fheis amounted to a 'done deal' in some respects, the political response last night was equally predictable. Sinn Fein can expect the British and Irish governments to accentuate the positive and use the ard fheis as the spur for the election they will confirm tomorrow.

For unionists, there is an element of the old proverb of being careful for what you wish for - in case you get it. Speaker after speaker yesterday emphasised the lack of appetite among unionists for republican involvement in policing, as a key reason for doing it.