Sara Canning, partner of Lyra McKee, walks behind her coffin as it is carried out of St. Anne’s Cathedral in Belfast on April 24. (Liam Mcburney/AP)

The murder of Lyra McKee, the young journalist killed by the “New Irish Republican Army” in Northern Ireland last week, has focused attention on how Brexit might affect Northern Ireland’s fragile peace. Whatever happens with Brexit, it has already weakened the 1998 Good Friday Agreement’s institutional fixes that led to paramilitaries dropping their arms. That has complicated an already difficult political situation.

Peace in Northern Ireland was already in trouble

The problems that Brexit poses for Northern Ireland are complicated by the fact that the Northern Ireland Executive and Assembly have been suspended since January 2017. That’s the locally elected government and legislature that were established as part of the Good Friday peace agreement.

That agreement brought an end to the Troubles, the 30-year civil conflict between unionists, who are predominantly Protestant and want Northern Ireland to remain part of the United Kingdom, and nationalists, who are predominantly Catholic and want Northern Ireland to be part of the Republic of Ireland. One of the agreement’s main provisions required them to share power in the Executive and the Assembly.

But in 2017, the main parties representing each side — the Democratic Unionist Party (DUP) and Sinn Fein — ceased working together, as the agreement required, leaving the province without a regional government. These fights were unrelated to Brexit. But Brexit — or more particularly, the heated atmosphere in British Parliament and among the wider public — has distracted the British government and kept it from pressuring the political parties in Northern Ireland to resolve their disputes. As a result, politicians have stopped engaging across sectarian lines. With no one to make policy decisions, the head of the Northern Ireland Civil Service told the BBC, there’s been a “slow decay and stagnation” in public services. Ordinary citizens have lost faith in government.

Relations between the British and Irish governments have worsened

The Brexit process has also damaged the relationship between the governments of Britain and the Republic of Ireland — a relationship that once provided a framework to accommodate Northern Ireland’s warring sides. But the two governments’ shared understanding has degenerated as they fight over the status of the border between Northern Ireland and the Republic of Ireland. Although all sides want to prevent violence from resuming, they differ on how to deal post-Brexit with the border, which — because both nations have been European Union members — currently has no passport or customs checkpoints.

That has to change if Britain leaves the E.U. At the Irish government’s insistence, the E.U. will only sign an exit deal if Britain agrees to keep the border open: In other words, traffic can continue to flow freely without passport and customs checks. Prime Minister Theresa May agreed to this “Irish backstop.” But Parliament has rejected the withdrawal deal three times — in no small part because many members of Parliament object to the backstop.

Pro-Brexit members of British Parliament argue that the Irish government’s position has made it impossible for Parliament to approve the withdrawal deal. These politicians seem willing to sacrifice the peace agreement in Northern Ireland if it allows them to exit Europe. The relationship between the two countries is as frayed as it has been in decades.

The British government depends on unionists to survive

Since the 2017 election in which May lost her majority in the House of Commons, she has depended upon the Northern Ireland Democratic Unionist Party’s 10 MPs to stay in power. The DUP is right-wing, fiscally frugal, socially conservative and ultra-unionist. It was also the only party in Northern Ireland not to sign the Good Friday Agreement — and the only party to actively campaign in favor of Brexit. Though it is the largest party in Northern Ireland, it only won about 36 percent of the vote in 2017.

The DUP’s role in propping up May’s party places it at the center of parliamentary debates over Brexit. Northern Ireland’s second-largest party, Sinn Fein, represents 29 percent of the vote and is staunchly nationalist. However, Sinn Fein’s seven MPs do not take their seats in Parliament because they refuse to recognize Britain’s sovereignty in Northern Ireland. These two facts lead to debate in Parliament that is profoundly skewed in favor of only one side of the historic conflict in Northern Ireland: the unionist perspective.

The Brexit process demonstrates how the Good Friday Agreement did not fundamentally erase the conflict’s divides — even if it did produce an arrangement that most Unionists and Nationalists could live with. Since McKee’s killing, the British and Irish governments have announced new talks among the Northern Irish political parties to restore the Assembly and the Executive. But it will have a hard time persuading them to work together given all the damage the Brexit process has done.

Kimberly Cowell-Meyers is an assistant professor in the School of Public Affairs at American University.

Carolyn Gallaher is a professor in the School of International Service at American University and the author of “After the Peace: Loyalist Paramilitaries in Post-Accord Northern Ireland” (Cornell University Press, 2007).