THERE WILL be limits to what President Obama can accomplish in foreign policy in his final months in office. He has already written off Syria, telling reporters Sunday he was “not optimistic about the short-term prospects” for stopping that devastating civil war. But in some areas, Mr. Obama not only will retain the capacity to act, but also will be compelled to address crises that cannot await the arrival of the next president. One of those is taking place in Congo.

Having already endured one of the bloodiest civil wars in modern times, the huge African nation faces a fateful moment on Dec. 19. That is when President Joseph Kabila is due to step down after two terms in office, the limit set by the constitution. Mr. Kabila is refusing to yield power and instead is maneuvering to remain in office indefinitely. Last month he struck a deal with a sliver of the opposition postponing elections until 2018; when visiting representatives of the U.N. Security Council asked him whether he would leave then, he suggested that the constitution could be amended to allow a third term.

Mr. Kabila’s intransigence is wildly unpopular among Congo’s approximately 80 million people. A poll conducted between May and September showed that 81 percent opposed changing the constitution to allow an additional presidential term, and 74 percent said the president should leave office on Dec. 19. Close analysts of the country say an explosion of protest is probable if Mr. Kabila does not step down by that day. The government could send the army to clear the streets; that could lead to a splintering of security forces that are an amalgam of regional and ethnic factions.

Mr. Kabila attempted to mollify the opposition with a “national dialogue” that led to the appointment of a new prime minister. But the most important opposition leaders rejected the process. Instead, they are supportive of a transition plan developed by civil society that calls for Mr. Kabila to step down by Dec. 19 and be replaced by the president of the Senate, a respected elder statesman, while new elections are organized. Mr. Kabila would be offered security guarantees.

Whether the president can be induced to accept this safe exit may depend on how the most powerful people around him perceive their interests. That is where the lame-duck Obama administration could have an impact. It has already imposed sanctions on two senior security officials for their role in human rights abuses, a powerful measure because of the use senior Congolese figures make of foreign bank accounts and travel. Yet it has delayed targeting other top officials, raising hopes in Kinshasa that the election of Donald Trump has eliminated the risk to their foreign assets.

A bipartisan group of House members is pressing the administration to move against those scheming to extend Mr. Kabila’s rule, including Vice Prime Minister Evariste Boshab and intelligence chief Kalev Mutond. That could deter other top officials from backing the power grab or following orders to suppress protests. As Rep. Christopher H. Smith (R-N.J.) put it in a Nov. 15 speech, “the pace and scope of sanctions need to match the urgency of the approaching electoral crisis.” Mr. Obama can and should act now.