LONDON — When Prime Minister Rishi Sunak held his first meeting with President Joe Biden, in Indonesia last November, he made Biden a welcome pledge: Britain would settle a trade dispute with the European Union over Northern Ireland by April, the 25th anniversary of the Good Friday Agreement.

That is the landmark peace accord that ended decades of sectarian bloodshed in the North — a prized foreign-policy legacy for Democrats and one that Biden would like to celebrate with a visit to Belfast, Dublin and possibly London in the spring, according to people familiar with the administration’s plans.

Now, with the anniversary less than four months away, Sunak faces a forbidding timetable to deliver on his pledge. The issues on the table remain as complex and politically fraught as they were for Sunak’s predecessors, Liz Truss and Boris Johnson, neither of whom came close to breaking the impasse.

On Tuesday, Sunak’s foreign secretary, James Cleverly, will travel to Washington, in part to brief Secretary of State Antony Blinken about the progress in London’s negotiations with Brussels. Those talks are expected to enter a decisive phase after a meeting Monday between Cleverly and Maros Sefcovic, the European Commission vice president who is its chief negotiator.

Both sides agree that the atmosphere for the negotiations has improved markedly since Sunak took office in October. The two sides recently struck a deal on the sharing of data, one of the technical issues that affect post-Brexit trade with Northern Ireland.

But the inescapable reality is that Brexit established a trade barrier between Northern Ireland and the rest of the United Kingdom, leading to cumbersome delays at customs checkpoints, and other thorny issues. Chief among them is whether the European Court of Justice, which guarantees that European law is applied in all member states, should have jurisdiction over the North.

This is viscerally opposed by hard-line Brexiteers in Sunak’s Conservative Party, who argue that it infringes on British sovereignty, and by unionists in Northern Ireland, who argue that it drives a wedge between them and the United Kingdom.

Sunak’s pledge to strike a deal by April came partly in response to pressure from Biden, who has put the Good Friday Agreement at the center of relations between the United States and Britain. U.S. officials argue that tensions over the status of Northern Ireland could jeopardize the hard-won peace there.

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This article originally appeared in The New York Times.