The United Nations commission and its partners must do more than stand their ground. So far, they have concentrated on a political purge in the capital, Guatemala City. To consolidate their gains, they must expand into Guatemala’s countryside, where the same criminal networks hold local politics hostage. But at present, the underfinanced attorney general has offices in only 10 percent of the country’s 338 mostly rural municipalities.

And there’s an even more fundamental challenge: It’s one thing to root out corruption; it’s another to create the functioning democratic and civil society that can inoculate a country against the disease. Guatemala is moving in the right direction, with growing numbers of citizens coming to understand that a democratic, equitable and just society is finally within reach. But to many, the government still seems incapable of decisive action; honest, enterprising Guatemalans don’t dare sign a government contract, and democracy activists hesitate to enter formal politics.

Failure could occur in any number of places. Political pressure and fear could force crusaders in government to resign. The United Nations may decide its job is finished and move resources elsewhere. American support could likewise dry up. Any stumble could lead to disaster, giving the momentum back to organized crime and crushing the public’s faith in peaceful change.

What happens in Guatemala matters far beyond its borders. The country is a test case in a region-wide battle against corruption. Reformers elsewhere are watching closely; if organized crime wins out, the illicit forces that govern much of Latin America will be buoyed. But if democracy succeeds, the region’s citizens will gain confidence, inspiration and know-how that can fuel their struggles to build the rule of law.

The United States government understands the stakes, and has vigorously supported the United Nations commission and the attorney general’s office. Their opponents, who accuse the United States of neocolonialism when it suits them, are hoping for a victory by Donald J. Trump in the fall, which may well lead to a cutoff in funds for the reformers.

But this support has also earned the United States crucial new allies. Liberal Guatemalans, even longtime die-hard opponents of American interventionism, have praised recent American efforts. After nearly a century of backing regimes notorious for oppression and violence, the United States is seen, finally, as being on the right side in Central America.

Like the reformers in Guatemala City, the United States can’t back down. Guatemalan organized crime is a major driver in the illicit flow of drugs, weapons and people northward. A partnership based on trust and good will among democratic neighbors stands a far better chance of keeping all of us much safer.