It isn’t hard to understand why Leo Varadkar is playing hardball in the Brexit negotiations. Only today has fresh evidence emerged that Ireland will be the country hardest hit by Brexit – and that includes the United Kingdom.

Given the volume of Irish trade that goes either to the UK or through the UK to European destinations, any sort of Brexit is going to create difficulties in Dublin. Hence the Irish Government’s push for Britain to remain as closely aligned with the Single Market and Customs Union as it can manage.

The deal the Government has struck with the EU over Ireland commits it to maintaining three things: “the all-island economy”; “north-south cooperation”, and “the Good Friday Agreement” (herein referred to as the Belfast Agreement unless quoting).

Unfortunately, the distinction between these issues is not quite so clear cut as all that. Here’s Tony Connelly, quoting an EU source for an RTÉ article:

“The deeper you go,” says one EU source familiar with the mapping exercise, “the more examples there are, more areas where you find out that actually a lot of the Good Friday Agreement requirements are more implicit than anything else. They rest on the status quo, and that status quo involves membership of the EU single market.”

Thus the moral authority of “defending the agreement” is too often adduced in support of policies, such as an invisible border, which actually have nothing directly to do with it as-written. And this ‘implicit’ dimension of the Belfast Agreement, which might as well constitute the ‘Invisible Clauses’, has enormous potential to undermine it’s cross-community support – amongst unionists.

Why? Because it twists the Agreement into something it wasn’t: an enshrined guarantee of the status quo offered by mutual EU membership.

When unionists voted to endorse the Agreement they were not voting to divorce themselves from UK foreign policy, nor to automatically acquiesce to an internal border between Ulster and the rest of their country.

Nor is it really possible to see how the Agreement could have offered any such guarantees. If any sort of tangible border between Northern Ireland and the Republic were a breach, how is the conjuring of a border between Ulster and the mainland not also one? If the Agreement guaranteed frictionless trade with the Republic, surely it would have to guarantee it to with the rest of the Kingdom?

Parity of esteem would surely demand as much, even before factoring in the obvious point (highlighted first on this site and lately in Hugh Bennett’s magisterial treatment of the subject on Brexit Central) that the mainland accounts for four times as much Northern Irish ‘external sales’ as the Republic.

Again, Varadkar is entirely within his rights to assert the Irish State’s interests in the negotiations. But if the Belfast Agreement is to survive as the basis for cross-communal self-government in Northern Ireland, it cannot go on being presented as a genie that grants nationalist wishes. (For a full list of the north-south issues the Agreement actually covers, check out the Annex to Strand Two.)

Unionists will otherwise be well within their rights to argue – where are our invisible clauses? What concessions to our British status does Dublin not yet know it has made? Or at the very least: why do our rights to be treated as part of the UK keep coming second to an “all-Ireland” alternative, despite nationalism’s failure to secure and win the referendum provided for in the Agreement to legitimise that alternative?

It doesn’t help that Connelly’s article reveals the persistence of another century-old Irish trope: that of Dublin and her international allies telling Ulster Unionists to sit down and stop complicating things. Consider this quotation, which with only a little tweaking might have been spoken by Woodrow Wilson:

“Unless Theresa May finds depths of courage and imagination,” says one senior EU source, “of which she has shown no signs so far, is she going now to do a brave and risky thing, and say to the DUP, listen you guys you’ve got nowhere else to go anyway, so this is what’s going to happen?”

Ironically, the EU could say the exact same thing to the Varadkar administration – Ireland is so hideously exposed to the consequences of a WTO-style Brexit that the idea that they would invite one by exercising a veto is not credible. If Michel Barnier can’t find the “depths of courage and imagination” to face down Dublin, why should Theresa May face down the DUP?

Moreover, why is it acceptable to treat Northern Ireland’s largest party, and the pre-eminent representative of one of its two major communities, in this dismissive fashion?

Of course, those pushing for Northern Ireland to stay in the Single Market and Customs Union are unlikely to abandon the sacralising language of ‘the Agreement’ and ‘the Peace’. It’s always nice to have one’s demands come robed as moral obligations, and the past twenty years have provided conditions which let the Agreement mean whatever the different sides wanted it to mean.

But it was not, and never has been, a guarantee of the full status quo ante, nor a basis for prioritising any and all of Northern Ireland’s links with the Republic over those with the mainland, in the face both of the Province’s clear economic interests and current constitutional status. The Agreement provides one clear basis for shifting to an all-Ireland default, and that is a referendum.

Varadkar will continue to push for Northern Ireland – or ideally for him, the UK – to remain “fully aligned” with the EU. This hapless Government may even accede to some of those demands. But if the idea takes root amongst unionists that the Belfast Agreement created a legal entitlement to all-Ireland arrangements which trumped their right to full participation in the United Kingdom, without a referendum, its legitimacy in that community would be, quite rightly, imperilled.