The White House has opened up a new front in the Brexit battle, suggesting Ireland and the EU have been disingenuous in negotiations.
Despite being feted on a visit to Dublin, US Vice-President Mike Pence used an appearance alongside Taoiseach Leo Varadkar to effectively back British Prime Minister Boris Johnson's hardline opposition to the backstop.
"As the deadline for Brexit approaches we urge Ireland, and the EU as well, to negotiate in good faith with prime minister Johnson," he said.
He asked that they "work to reach an agreement that respects the UK's sovereignty and minimises disruption to commerce".
The Trump administration has long been a supporter of Brexit - but there was still surprise that Mr Pence would issue such a strident statement while in the company of Mr Varadkar.
Mr Pence was speaking just moments after the Taoiseach had asked him to bring an understanding of the Good Friday Agreement and the backstop back to Washington.
The return of a hard border was called a "very real risk" by Mr Varadkar. He said Brexit could create barriers to co-operation and risk peace.
"We as a Government have to stand our ground on the agreement," Mr Varadkar said.
"All I ask is that you bring that message back to Washington with you.
"This is not a problem of our making. It is one we want to solve - through an orderly Brexit and a Withdrawal Agreement that guarantees no re-emergence of a hard border on this island."
Sources say the Taoiseach repeatedly explained Ireland's attachment to the backstop during a private 30-minute meeting with Mr Pence.
One official told the Herald that Mr Pence appeared to have a "good understanding" of the issues and the Government's "commitment to the Good Friday Agreement".
However, other Government sources admitted Mr Pence's comments were not what they would have hoped for under the circumstances.
Earlier, Mr Pence and his wife Karen were greeted by Mr Varadkar and his partner Matthew Barrett at the front door to Farmleigh, the State guest house in Phoenix Park.
The vice-president signed a visitor book before lunch with the Taoiseach, Mr Barrett and Mr Varadkar's parents, Ashok and Miriam.
Mr Pence is a conservative who opposed gay marriage during his time in Congress.
The vice-president was greeted by President Michael D Higgins and his wife Sabina at Aras an Uachtarain yesterday morning.
The Pence family had spent their first night of their Irish visit in Doonbeg, Co Clare - a place the vice-president has family links to.
Last night, Mr Pence visited Morrissey's pub in Doonbeg for dinner.
He met locals, telling them about his time working in the pub in 1981, which is near the home of his great-grandmother.
When asked if he would pull a pint, the vice-president said: "I don't think I would remember how."