Ever since the Brexit vote, Ireland has had the rest of the European Union behind it in insisting there can be no hard border with Northern Ireland when Britain leaves.
But with a draft UK-EU deal that would guarantee an open border looking increasingly frail, and the growing risk that Britain could withdraw from the union with no agreement at all, cracks are starting to emerge.
Over months of talks, both Dublin and Brussels have been loath to spell out the implications of having to carry out EU customs and regulations checks on what would become the bloc's new frontier.
A comment from the European Commission's chief spokesman Margaritis Schinas earlier this week shattered the taboo.
"In a no-deal scenario in Ireland, I think it's pretty obvious, you will have a hard border," he said.
The remark caught Dublin off-guard and the government pointed to EU promises to keep the border open.
The Irish Independent branded Schinas's comments a "Brexit backstab", suggesting they were intended "to prepare Dublin for some difficult discussions in the weeks ahead".
Schinas softened his remark the following day, saying the EU would do "all it can" to avoid a hard border.
But Ireland, which considers itself an unwilling bystander to Britain's decision to leave the EU after 46 years, is feeling under pressure to compromise over its demands.
"Why is it the country being victimised that's always being asked to give?" Prime Minister Leo Varadkar asked in an interview with Bloomberg TV on Friday.
- Cooling comments -
Varadkar has come under some domestic criticism for failing to prepare for the possibility of a hard border.
But Federico Fabbrini, director of Dublin City University's Brexit Institute, said the government's position was "reasonable".
"It doesn't want to take action on the border for as long as reimposing a border is avoidable," he said.
EU chief negotiator Michel Barnier sought to de-dramatise the concerns, but only raised more questions.
"We will have to find an operational way of carrying out checks and controls without putting back in place a border," he said.
The EU-UK deal includes a "backstop" plan to keep the border open by keeping Britain tied to EU trade rules, but Brexit supporters in London hate it.
They seized on Barnier's comments, saying they proved the backstop was not needed to prevent a hard border.
The backstop is a major block in getting the Brexit deal agreed by the British parliament, and London is pressing the EU to modify the plan.
After months of seeming like the consistent and mature voice in Brexit negotiations, Ireland now risks appearing the stubborn obstacle to a smooth Brexit.
- 'A period of chaos' -
Varadkar this week also warned that a no-deal would lead to a "period of chaos" and that ultimately the EU, Britain and Ireland would have to "agree on full alignment" between Northern Ireland and the Republic to avoid a hard border.
What that chaos might look like and how the EU-brokered accord would function on the 310-mile (500-kilometre) border traversed by more than 200 roads is hard to say.
Brexiteers in London say checks on the border could simply be replaced by trusted trader schemes and as-yet-untested technology.
Speaking in Davos on Friday, Varadkar said it could "involve people in uniform" -- as well as "cameras, physical infrastructure, possibly a police presence, or an army presence to back it up".
That would be a concerning development on a border where the last military checkpoints were dismantled 20 years ago after a peace accord ended three decades of conflict.
Given Ireland's refusal to prepare for a hard border, there could also be days or even weeks when the frontier is effectively ungoverned by international law.
"You could have hundreds of lorries parking up at the border awaiting some kind of clearance," said Seamus Leheny, policy manager of the Freight Transport Association in Northern Ireland.
"We could be left in a situation where some hauliers will have to take the decision to turn away any freight going across the border. The concern they have is they technically could be seen as smuggling."
