Northern Ireland Deputy First Minister Martin McGuinness, left, U.S. President George W. Bush, center, and Northern Ireland First Minister Peter Robinson, right, during a meeting at Stormont Castle in Belfast, Northern Ireland in June 2008. Photo credit: White House photographer Chris Greenberg

Former President George Bush reportedly appealed directly to Conservative leader David Cameron to support the Northern Ireland peace process last week, The Guardian reported in an exclusive today, marking the former president’s most active intervention in global politics since leaving the White House.

According to The Guardian, Bush asked Cameron to “press his unionist partners to endorse the final stages of the 15-year search for a settlement.” It didn’t work: The Ulster Unionist Party declared last night that it would vote against the devolution of policing and criminal justice authority to Northern Ireland.

The Telegraph noted that Bush allegedly felt that a “conservative to conservative” pep talk could influence Cameron to put greater pressure on Sir Reg Empey, leader of the UUP. According to the paper, Cameron, who “pointedly distanced himself from American foreign policy” during Bush’s presidency, replied that he couldn’t order local parties to tow the line.

Even so, Sir Reg accused officials of trying to blackmail and bully the party into signing on to the deal, The Telegraph reported today.

A no vote from the UUP isn’t enough to sink the whole deal – the UUP is the only member of the four-party power sharing executive body that is refusing to go along with devolution – however, The Guardian reported, political leaders fear that it would be enough to undermine support for the deal among other unionist ranks.

The US has been deeply involved in the Northern Ireland peace process since President Bill Clinton’s high-profile involvement in the early 1990s, so much so that a group of US Congressmen wrote to Cameron last month out of concern that a failure to get all of the unionists on board could “embolden” dissident terrorists. America is also a bit in for a penny and certainly a pound now, have invested heavily in Northern Ireland. Henry McDonald, The Guardian’s Ireland correspondent, wrote today that America holds the key to peace in Northern Ireland and claimed that while Bill Clinton pushed the peace process along in a very public way, it was Bush who drove it politically.

And what about David Cameron? The Guardian, in a leading editorial today, wrote that Cameron now finds himself heading a party that started and supports the Northern Ireland peace process and partnering with a party that could totally derail it, ahead of a general election no less. Said The Guardian, “Mr Cameron needs to decide which side he is on: the peace process or those who want to derail it. He can’t be on both.”