FROM TIME to time, Haiti’s chronic political dysfunction erupts in crisis and violence, compelling the international community to re-engage with an impoverished country it might prefer to disregard. Haiti is at just such a juncture right now. Policymakers in Washington and elsewhere should pay prompt attention, before the predictable calamity arrives.

The brewing crisis arises from a three-year-old political impasse between President Michel Martelly and legislators that has blocked parliamentary and municipal elections. An election date came and went, triggering mounting protests and street violence in recent weeks.

Now the clock is ticking toward what looks like a watershed. On Jan. 12 the terms of most members of parliament will expire. In the absence of a duly elected parliament, Mr. Martelly will be empowered to rule by decree, a dangerous scenario in a country with a history of autocracy and instability.

Some lawmakers in the politically fractured parliament think Mr. Martelly, elected in 2011, has been angling all along to establish a de facto dictatorship. In fact, parliament shares the blame. A group of six senators has blocked legislation to establish an electoral council on the grounds that its composition and rules would favor candidates loyal to the president. With no council in place, elections are off the table.

To his credit, Mr. Martelly tried to break the impasse this month by forcing the resignation of his prime minister and close political ally, Laurent Lamothe. Mr. Lamothe, a wealthy businessman, was widely seen as Mr. Martelly’s hand-picked successor for president; the hope was that his departure would clear the way for a compromise between the president and the opposition, leading to elections.

So far that hasn’t happened. If a vacuum develops, Mr. Martelly will be the last man standing; he says he’s prepared to lead by decree if no deal is struck leading to elections. Even the president’s moderate opponents say that would trigger a wave of violence.

Recognizing that the standoff has become dire, Secretary of State John F. Kerry has urged a negotiated settlement that would “open the door for elections to be scheduled as soon as possible.” Yet without more aggressive mediation by U.S., United Nations, French, Canadian and other diplomats, the chances of such a settlement are slim.

As it happens, the senators’ terms will expire and parliament will be dissolved on the fifth anniversary of the earthquake in 2010 that killed more than 100,000 Haitians. As Mr. Kerry pointed out, too much progress has been made since then toward rebuilding Haiti to risk extinguishing all hope amid renewed political violence.

To dismiss Haiti as a basket case or shrug off its troubles as insoluble is to forget a history that suggests that without outside help, the country can deteriorate into anarchy, at which point ignoring it is no longer an option.