Ministers are increasingly concerned the new US congress will side with Dublin in any Brexit dispute over the Good Friday Agreement, Sky News has learned.
Cabinet sources have pointed to the Democratic takeover of the House Committee on Ways and Means.
It is responsible for supervising the post-Brexit US-UK free trade agreement, so sought after by Brexiteer politicians.
Some Conservative MPs have, in direct consultations with the Prime Minister at Number 10, made the exact opposite case.
They have asked Prime Minister Theresa May to contact US President Donald Trump to use his leverage with the Irish government to change or junk the backstop.
That is the insurance policy to prevent a hard border reforming on the island of Ireland if a trade deal with the EU cannot be sealed in time.
But Sky News understands that there is alarm among UK cabinet ministers that should any British government be seen to renege on commitments to Dublin, the Irish lobby in Congress could make life very difficult in vital trade talks with the US.
Early consultations on that deal have already begun on Capitol Hill.
Last week, a member of the committee, representative Brendan Boyle, told Sky News: “We are very sensitive about anything that could possibly threaten the Good Friday Agreement, so specifically that the backstop was removed – the thing that was guaranteeing that there would be no return to a hard border on the island of Ireland.
“That is concerning to many of us on Capitol Hill.”
Congressman Boyle last week tabled a resolution in the House of Representatives demanding that the open border in Ireland is protected through the Brexit process.
Alongside the Chair of the ways and means committee Richard Neal he met with Brussels’ chief Brexit negotiator Michel Barnier last year.
Speaking to Sky News after the prime minister instructed her MPs to vote against the backstop she negotiated in the Commons, congressman Boyle made a connection with a prospective trade deal.
“If you renege, or you go back that does not affect just this current issue, but all future issues, you lose your credibility,” he said.
“So the next step after hopefully the UK and the EU finally come to terms and get an agreement passed is that we’re going to be looking at the US and UK trade deal, so we will remember how good one’s credibility is.”
The ways and means committee have in the past instructed the renegotiation of trade deals negotiated by the US government.
New chairman Richard Neal is a longstanding and leading supporter of the Irish Republican movement, and the peace process, who invited former Sinn Fein leader Gerry Adams to the inauguration of president Obama in 2008.
Just a few months ago he accompanied Sinn Fein politicians to the border area alongside “Border Communities Against Brexit”.
He recently recalled being on a cross-border bus searched by British army crossing the border during the Troubles.
The Irish Deputy PM Simon Coveney is visiting Washington DC this week, including the key figures in Congress.
(c) Sky News 2019: Ministers fear Irish lobby influence over US post-Brexit trade deal