Failed U.S. Presidential candidate Hillary Clinton has again intervened in the Brexit process, praising the European Union (EU) and claiming the peace in Northern Ireland is jeopardized by the UK’s divorce from the bloc.

Clinton, who made her opposition to Brexit known during her presidential campaign, claimed that border checks in Ireland would be an “enormous setback” – implicitly backing the UK staying tied to many of bloc’s rules inside the Single Market and Customs Union.

Mrs. Clinton’s husband, former U.S. President Bill Clinton, is expected to visit Northern Ireland this week to join celebrations of the 20th anniversary of the Good Friday Agreement, which he helped to negotiate.

“These are difficult times for Northern Ireland, and for our world,” Mrs. Clinton wrote in The Guardian on Tuesday. “As the Brexit debate rages on, I continue to believe in the value of the European Union, and of a Europe that is whole, free and at peace.

“But no matter the outcome of these discussions, we cannot allow Brexit to undermine the peace that people voted, fought and even died for. Reinstating the border would be an enormous setback.”

The EU has also said they will not accept border checks, and Prime Minister Theresa May agreed with the bloc in December to keep Northern Ireland in “regulatory alignment” with the Single Market to keep the border open.

Brussels Official: UK Will Be ‘Protectorate’ of EU Under Appeaser Theresa’s Brexit Plan https://t.co/LAEmFkWinf — Breitbart London (@BreitbartLondon) December 7, 2017

However, the Democratic Unionist Party (DUP), which potentially has the power to block the final Brexit deal, has said it will not accept the province leaving the EU on different terns to the rest of the UK.

It is unclear, therefore, how the UK can free itself of EU Single Market rules, such as the free movement of people, without introducing some border checks.

Mrs. Clinton backed the EU’s position, claiming that “reinstating the Irish border would be an enormous setback”, and by implication gave her support to a “soft Brexit” linked to the Single Market.

Border checks, she said, would be like “returning to the ‘bad old days’ when communities would once again be set apart”, claiming the Good Friday Agreement could be threatened.

“Countless people in Northern Ireland are alive today, rather than in early graves, because of it,” she added.

However, some Brexiteers, such as Foreign Secretary Boris Johnson, have argued that the EU and anti-Brexit campaigners are manipulating the issue of the Irish border in an attempt keep the UK tied to many of its rules and regulations.

Chairman of Parliament’s European Research Group, Jacob Rees-Mogg MP, said last month campaigners were intentionally making an issue out of the complex history of the Irish border to whip up fear about a return to violence.

He said: “There is huge desire of all parties to maintain the peace in Northern Ireland and I fear that the risk in Northern Ireland is more from the inability to get the government back up and running than it is from issues relating to the border which the EU is using to try and keep the UK in the Single Market and the Customs Union.”

Mr Rees-Mogg has said a high-tech solution to the border is possible, allowing for control without the need for “men in peaked caps” to stand by the frontier.