ON THE last day of 2016, the Catholic Church announced a remarkable political breakthrough in Congo, a sprawling country nearly the size of Western Europe that for decades has been a fount of war and instability in Africa. Joseph Kabila, the country’s president since 2001, had refused to leave office after the expiration of his second term in December, bringing Congo to the brink of another violent upheaval. The accord brokered by the church called for new elections in 2017 in which Mr. Kabila, who is constitutionally barred from seeking another term, would not take part; in the meantime, a new prime minister would be chosen by the opposition coalition.

More than two months later, the deal seems to have unraveled — and Congo is again on the edge. Mr. Kabila, who never signed or publicly endorsed the accord, has retreated into his customary seclusion even as his security forces conduct a violent crackdown. As the Wall Street Journal reported, government forces have killed some 180 people since Dec. 31, including scores in the Kasai-Central province, the stronghold of the opposition Union for Democracy and Social Progress. A video circulated by human rights groups last month appeared to show a massacre by government soldiers of at least 13 people, including several women; a U.N. official said as many as 101 people, including 39 women, may have been killed in Kasai.

Last month the U.N. Security Council condemned the new violence, which it said may constitute war crimes. It called on the government to revive talks on implementing the Dec. 31 agreement, including the nomination of a new prime minister. On Monday, a draft European Union document warned of new sanctions against those “responsible for grave human rights violations, for inciting violence or obstructing a peaceful resolution of the crisis.”

The international response is salutary but it is unlikely to be successful unless it is fully joined by the United States. After some hesi­ta­tion, the Obama administration played a significant role in bringing pressure on the Kabila regime, punishing some of its top leaders for involvement in human rights abuses. The Trump administration, however, has shown little interest in promoting democracy and human rights or, for that matter, Africa; the State Department’s reaction to the alleged massacre in Kasai was a perfunctory statement. The White House’s only Congo-related action has been a reported draft executive order lifting controls on the trade of minerals that have been used to fund armed groups.

Mr. Kabila may be betting that Mr. Trump will shrug if he scraps the political accord and uses force to remain in power. So the administration should move swiftly to signal its readiness to join new E.U. sanctions. Mr. Kabila’s intransigence risks touching off another explosion of bloodshed in Central Africa — something that even an “America First” president should want to stop.