At stake now is not just the ideological future of unionism, but the Union itself.

In past elections unionist parties – and most recently the DUP – have talked up the constitutional threat for their own advantage. No longer.

Now the future of the United Kingdom is imperilled from myriad directions – and some of those are entirely beyond Northern Irish unionists’ control.

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The decisive national outcome of the general election leaves the DUP with no leverage at Westminster. As a consequence, it now faces a rapid move towards an Irish Sea trade border.

Having backed Brexit as something which would improve things, the DUP now finds that for which it dreamt and campaigned threatening to unravel the Union itself.

Brexit itself and the DUP’s support not only for leaving the EU, but for a harder form of Brexit, was a key factor in the de facto nationalist and Green Party pacts in North Belfast and South Belfast which cost it two seats.

The loss in North Belfast of Nigel Dodds, the party’s Westminster leader and one of unionism’s elder statesmen, is devastating.

On Thursday night as it became clear that his seat was in jeopardy, one DUP member sent me a message saying: “We could lose anyone but him.”

Few people across the DUP’s disparate and frequently warring factions would disagree with that sentiment.

Not only is he a strategic asset to the DUP and a respected figure at Westminster in a way that some of his DUP colleagues are not, but his defeat speaks to a profound psychological problem for unionism.

This seat, once held by the father of Ulster Unionism, Edward Carson, has never been held by a nationalist before – still less by a republican.

As such, Mr Dodds’ defeat represents an old certainty which now is slipping away from unionism.

And as the latest in a line of once impregnable unionist seats which have been lost by unionism, the result is evocative of a wider sense that not only control of Northern Ireland – but potentially Northern Ireland itself – is slipping away.

There is no inevitability that a united Ireland is coming. Just four years ago, prior to Brexit and the collapse of Stormont, polls pointed to Northern Ireland being more constitutionally secure than at any point since its creation in 1921.

And even in this election, where unionism has suffered a grievous blow, Sinn Fein’s vote has fallen further than that of the DUP.

The rise of the Alliance Party, astonishingly in this election the third largest party, is no guarantee of support for Irish unity.

But it is a clear rejection of what has seemed like an archaic form of unionism whose biggest idea often seems to be to circle the wagons with an electoral pact when seats come under pressure.

Yesterday the man who is seen by some DUP members as the great hope of unionism said something which appeared to misunderstand the core problem.

Asked on Good Morning Ulster about the psychological damage of the result for unionism, Sir Jeffrey Donaldson referred to “the splintering of the unionist vote, for example, in places like North Down” and said that unionists wanted unity.

It is a measure of how far unionism has fallen that a sentence like that can be uttered without drawing gasps.

North Down is one of the safest unionist seats in Northern Ireland. Less than a decade ago, unionists won 90% of the votes there.

If a unionist pact is required to stop it being lost, that is a pitiful reflection on the state of the DUP and UUP.

The logic of suggesting a pact in North Down is that there is almost no winnable seat which the UUP should contest without a pact.

But while that would suit the DUP’s short-term interests – and perhaps even those of the UUP if it gained a seat as a result – the evidence suggests that pacts are one of the reasons that Alliance is surging.

Facing a developing fire, a move towards widespread unionist unity could act as an accelerant.

Unlike nationalism, where Sinn Fein has – despite its major victory in North Belfast – had a poor election but has seen votes largely slip from it to the SDLP, this election has confirmed the complete dominance of the DUP within unionism.

With that dominance comes responsibility when unionism falters.

Will Arlene Foster accept that she is either accountable or responsible for any of this crisis? Or will she blame everyone but herself?

History suggests the latter, despite the fact that DUP members privately say that many voters expressed their unhappiness at Mrs Foster during canvassing.

For a party renowned for its bare-toothed ruthlessness, the DUP has been remarkably understanding of the failures on Mrs Foster’s watch.

There was an abortive putsch after she led unionism to the first loss of its Stormont majority in the history of Northern Ireland.

Those who quietly muttered about challenging her then but chose not to do so must now wonder if they could have helped prevent this catastrophe for unionism.

Unionism now lacks a strong leader at the point where it needs one most.

Loyalists – including paramilitaries – poured into political activism their efforts at rejecting Boris Johnson’s Irish Sea border. Now that strategy has failed, where do they go?

Some, based on the recent meeting in Portadown from which my colleague Ben Lowry reported, will be arguing for street protests, if not outright violence.

Even setting aside moral considerations, past loyalist violence has been strategically disastrous and the street disorder during the flag protests actually boosted Alliance’s vote.

Unionism stands weary at another crossroads. But unlike the choice between Terence O’Neill’s moderation and the full-throated unionism of Paisleyism 51 years ago, this time the possibility of a vote for Irish unity is more real than many then could conceive.