America's role in the peace process is often misunderstood, including it seems by Philadelphia Democrat congressman Brendan Boyle, who last week tweeted: "The United States is, by law, a guarantor of the Good Friday agreement. We will not stand idly by and watch it weakened or destroyed."
Boyle is a member of the committee that must approve any post-Brexit UK trade deal, so he could be a significant person in our future.
His tweet caused much head-scratching as the United States is not a signatory to the 1998 peace deal, nor is it referenced in the text in any way. Congress has passed resolutions supporting the agreement, most recently last year, but these are not laws in the United States, let alone in Northern Ireland.
If some in Washington now sees Brexit as leveraging their influence against London and unionism, they should at least understand what a sudden and total reversal of America's role that represents
Boyle appears to be taking international treaties as seriously as the UK government and he is hardly alone among influential Washington politicians. Making stuff up about the Belfast Agreement is a game now well established on both sides of the Atlantic.
As a result, an old feeling is re-entering Northern Ireland of America, specifically Irish-America, as an active, partisan participant in our politics.
This is a tragedy for everyone who worked for decades to make that feeling go away.
Unionist hostility towards the United States was a defining sentiment of the Troubles and its complete disappearance was one of the peace process’s least appreciated achievements: I recall how unsettling it felt to think of all the power and money pointed towards bombing your town. Some people seemed more enraged by it than by the violence itself.
Starting in the mid-1970s, SDLP leader John Hume built a high-profile Washington coalition to focus Irish-America on constitutional nationalism and away from tin-rattling for the IRA. Hume's agenda was shared by successive Irish governments and was enormously successful within the United States.
However, it could not remove tensions over US involvement in Northern Ireland while the bombs kept exploding and Irish-America kept producing pro-IRA organisations and politicians – some of whom, like New York congressman Peter King, are still around and muscling in on the Brexit debate.
The 1994 IRA ceasefire drew out much of this poison, replacing it with unionist fears and nationalist hopes of pro-active American involvement. That appeared to be borne out when Gerry Adams was granted a US visa less than a month later, yet the Sinn Féin leader did not have the triumphal tour many were expecting. The position of President Bill Clinton's White House, revealed later to the BBC - was "engage with him or show him to be a fraud".
Books have been written about the high-wire diplomacy behind the visa and Anglo-American relations were apparently strained for years.
For most people in Northern Ireland, however, it seemed America was finally discovering the fraud and complexity of everyone’s positions and being driven to a more neutral stance as a result.
By the time Clinton made his landmark visit to Belfast in 1995, a huge cross-community crowd thronged the streets to hear him.
US involvement then settled into an unexpected pattern. America’s role became one of leaning on Sinn Féin to rein in the IRA.
In the three years leading up to the Belfast Agreement, the IRA broke its ceasefire by bombing London and committing other violence in Northern Ireland to try and gain leverage in talks.
Clinton ensured this did not succeed – that was America's most direct input into the 1998 deal, alongside the chairmanship of former US senator George Mitchell.
Washington took an even firmer line against Sinn Féin under president George W Bush. After 9/11, Bush's special envoy Richard Haass applied fierce personal pressure on Adams to end continuing IRA activities.
In 2005, Adams was banned from the White House and Sinn Féin was banned from US fundraising over the Northern Bank robbery and the murder of Belfast man Robert McCartney. IRA decommissioning and disbandment quickly followed.
Police republican areas
The last part of the peace process to be settled was the devolution of policing and justice. Bush stopped Tony Blair’s government from allowing Sinn Féin to police republican areas via IRA so-called “restorative justice” schemes, as Washington considered this an extraordinary abrogation of law and order.
Leaning on London for going too easy on the IRA was quite a turnaround from the first Adams visa.
President Barack Obama continued sending special envoys and talks chairmen, including Haass.
Hillary Clinton provided a fascinating codicil on America's role when she visited Belfast as foreign secretary during the 2012 loyalist flag protests. Condemning the violence, she admitted there was little she could do about it apart from perhaps offering loyalists money. American leverage had come to be seen as something that only worked against Irish republicans.
If some in Washington now sees Brexit as leveraging their influence against London and unionism, they should at least understand what a sudden and total reversal of America’s role that represents.
Such a dramatic change should be handled with care.