Two years ago, Guatemalans succeeded in pushing then-President Otto Perez Molina and Vice President Roxanna Baldetti out of office for corruption, thanks to the help of the U.N.-backed International Commission Against Impunity in Guatemala, or CICIG. Through its investigations, which brought thousands of protesters out into the streets, the commission found that Perez Molina’s administration had led a high-level graft ring, taking bribes from international businesses rather than collecting taxes for the state. Both leaders are currently in prison.

It was an unprecedented moment of accountability for a country that suffers from high rates of impunity. But it was just the start of a struggle between CICIG and Guatemala’s entrenched political class. It came to a head last week when President Jimmy Morales, a career comedian and political outsider who was elected after Perez Molina’s resignation, declared Ivan Velasquez, the Colombian judge who has headed CICIG since 2013, persona non grata and ordered him to be expelled from the country. ...