The latest intervention by House Speaker Nancy Pelosi in the Brexit debate has significantly raised the stakes when it comes to Britain’s future trade relationship with the United States.

On Wednesday, the top Democrat in the US House of Representatives issued a statement warning that Brexit “cannot be allowed to imperil the Good Friday [Belfast] Agreement”. She said there would be “no chance” of Congress passing a US-UK trade agreement if Brexit undermined the peace accord.

Her intervention – reinforcing comments she made to The Irish Times last month following the appointment of Boris Johnson as UK prime minister – were a direct rebuke to John Bolton, president Donald Trump’s national security advisor. In London this week, he said that Britain would be “front of the trade queue” when it came to reaching a deal with the US – his language an obvious riposte to former president Barack Obama’s warning ahead of the June 2016 referendum that Britain would be “at the back of the queue” if it voted to leave the EU.

The new government in London has been enjoying something of a honeymoon period with the Trump administration. Britain has traditionally had close connections to Republican power-players in Washington, due in part to its tradition of military alliance. Bolton in particular was a central player in the early 2000s when Tony Blair famously backed the Bush administration’s incursion into Iraq on evidence that was later discredited. Trump has publicly praised Johnson and the two men have spoken several times by phone since Johnson’s arrival in Downing Street.

Bolton’s pledges delivered in London came just a few days after a group of Republican senators signed a letter of support for Boris Johnson. The letter was initiated by Tom Cotton – the same Arkansas senator who blocked a Bill opening E3 visas to Irish citizens last year – and was signed by 44 of his Republican colleagues. Invoking the words of Winston Churchill, the letter promises a new bilateral trade agreement with Britain “as early as your Brexit terms would allow, that reflects the centuries of open commerce between our nations”.

While the display of warm wishes was something of a diplomatic coup for British officials in Washington, the intervention by Pelosi will be a major cause for concern.

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Colombia precedent

Pelosi’s power is not to be underestimated. When it comes to trade, she has seen this movie before. In 2008, the Democratic-controlled Congress plunged Washington into a crisis when it refused to back a US-Colombia trade deal proposed by George W Bush. The House Speaker at the time was Pelosi. Since the 1970s, free-trade agreements in the US had been handled by a fast-track procedure allowing a simple up-and-down vote. But in April 2008, Pelosi invoked a rarely used legislative tool that allowed the House to deny that fast-track procedure to specific Bills. The result was that the US-Colombia trade accord was ultimately treated like other legislation, and delayed for years.

Pelosi’s decision to intervene may be seen as an attempt to remind the Trump administration of the legislative branch’s constitutional muscle when it comes to trade

This tool remains open to the Democratic-controlled House of Representatives today. Any free trade agreement proposed by the Trump White House will have to be approved by a single majority in both Houses of Congress. The first step will be a vote in the Ways and Means committee – chaired by the co-chair of the Friends of Ireland caucus, Richard Neal. But the ratification process is unlikely to even reach that stage if Democrat demands are not met in advance.

Given Pelosi’s grip on her caucus and ability to whip votes, few Democrats are likely to break with the Speaker if her demands about the Belfast Agreement are not met.

Pelosi’s decision to intervene in the deepening standoff over a possible post-Brexit trade deal between the US and the UK may be seen as an attempt to remind the Trump administration of the legislative branch’s constitutional muscle when it comes to trade. The House of Representatives and the executive branch are already struggling to agree the USMCA, a revised version of the US-Mexico-Canada Nafta trade agreement which is relatively uncontentious.

Unrealistic MPs

Pelosi’s motivation may also be personal –her grandchildren spend a lot of time in Ireland. She has also been close to Neal, the predominant voice on Irish America on Capitol Hill, for decades.

The reality is that a US-UK trade deal will not happen without the support of the House Speaker

Jeffrey Schott, a trade expert at the Peterson Institute in Washington, believes that senior British politicians such as Dominic Raab and Liz Truss who visited Washington last week have unrealistic expectations when it comes to trade. “Both the US and UK governments want to pursue trade talks but the senior officials clearly underestimate what is required to put a deal together and how long it would take,” he says, noting also that Britain has outsourced most of its trade policy to the EU in recent decades.

Despite the boost from Pelosi this week, there are still challenges ahead for Ireland. Irish officials in Washington, who have strong contacts on Capitol Hill, have been upping their engagement with staffers in Congress since the publication of the Cotton letter. The fact that vice-president Mike Pence will visit Britain for two days next month just ahead of his visit to Ireland is also worrying, given that he is likely to meet senior figures in the British government who have sought to downplay the impact of Brexit on Northern Ireland.

The reality, however, is that a US-UK trade deal will not happen without the support of the House Speaker. For Ireland, it is fortuitous that Pelosi has the interests of the people of Northern Ireland at heart.

Suzanne Lynch is Washington Correspondent