Within days we will have a clearer idea if this Conservative UK government is as unionist as it seems.
As early as Monday it might be apparent whether or not Dublin’s insistence that there will be no hard Irish border has prevented a move to the next stage in the Brexit talks.
What has become an international drama over the frontier is now in its most critical phase.
Last night the Financial Times was reporting major EU-UK progress on the impasse.
But the language from the European Council president Donald Tusk still sounded hardline yesterday evening when he emerged from a meeting with Leo Varadkar in Dublin to warn Theresa May that she must satisfy Irish demands if the talks are to move forward.
Mr Tusk vowed to consult the Taoiseach on any British proposal before deciding whether to recommend EU leaders give the green light to the second phase of Brexit talks, including discussions on a free trade deal.
“If the UK offer is unacceptable for Ireland, it will also be unacceptable for the EU,” he told a joint press conference.
“I realise that for some British politicians this may be hard to understand, but such is the logic behind the fact that Ireland is an EU member while the UK is leaving.”
That is almost as tough as the language has been in this dispute.
But if you look more closely at what is being said, there appears to be a softening in Dublin’s position.
Last week in this column, see link below, I cited a talk that I had been at days previously in Belfast by Simon Coveney, then the Irish foreign minister and now its deputy prime minister.
In essence, Mr Coveney said then that if there was any regulatory divergence between Northern Ireland and the Republic, his government “would not stand for it”.
That was setting the scene for a major crisis, because it would have meant NI had to leave the single market and customs union. This would necessitate a border in the Irish Sea.
But since then The Times has reported that the government is considering convergence in some areas such as agriculture and electricity.
Mr Coveney yesterday told BBC Radio Four that the current level of north/south co-operation cannot be maintained if there are different standards in relation in areas such as “food safety, animal welfare...”
The very fact that Mr Coveney was mentioning particular areas seems to be a retreat from an insistence that the Province stay fully in the single market and customs union.
And his article in this newspaper today, see link below, specifically says that Dublin is proposing “nothing that remotely threatens Northern Ireland’s constitutional status”.
While it is unclear what exactly he means by this, he must realise that a departure from the single market and customs union is undeliverable from London.
Sammy Wilson MP made clear that the DUP would not accept such an arrangement. It seems, from our reports today, that might also be the party response to specific areas in which there are convergence.
What would specific areas of convergence mean in practice? What precisely would the constitutional implications be?
The idea certainly seems worthy of consideration and debate.
In recent years, Jim Allister has been concerned at the implications for the Union if Northern Ireland has different tax rates to Great Britain if a lower rate of corporation tax for NI is ever introduced.
But that proposal ended up getting cross-community support. Latterly it was Sinn Fein that seemed ambivalent about that tax plan.
In recent weeks unionists have had reason to take comfort from London’s response to this row with Dublin over the border.
Leading Tories such as Lord Hague have made clear that the Conservative government would not countenance a border in the Irish Sea even if the administration was not dependent on unionist MPs.
The great anger in London towards Dublin over the threat of blocking the Brexit negotiations might have unnerved Mr Varadkar, even though he is adamant that his government will not back down.
The EU seems keen to press ahead to the next stage, now that Britain’s financial settlement has been agreed in outline.
We will discover perhaps as early as Monday whether or not the Conservatives have been as emphatic on the other major outstanding matter, the constitutional integrity of the UK, as to date it has seemed.
• Ben Lowry (@BenLowry2) is News Letter deputy editor