Protesters call for the impeachment of Peruvian President Pedro Castillo in Lima, Peru, Aug. 5.

Photo: Carlos Garcia Granthon/Zuma Press

Guerrillas slaughtered 16 people in a south-central Peruvian village in May. The BBC reported “the bodies had bullet holes” according to a local official, and some, “including those of two children, had been burned.”

The Central Committee of the Militarized Communist Party of Peru, an affiliate of the Maoist-inspired Shining Path, “left pamphlets at the scene ordering people not to vote in the upcoming presidential election,” the BBC said.

Had the Shining Path known that a sympathizer to its cause would be declared the winner of that election, and would fill his cabinet with fellow travelers, perhaps it would have skipped that massacre. Terror is the tool of the Shining Path but power is the goal.

In President Pedro Castillo of the Marxist Perú Libre party, Peru’s narco-guerrillas may believe they have found a legitimate path to totalitarian rule. Most of the rest of the country disagrees.

An early accomplishment of Mr. Castillo is that he has united Peru’s center right and center left. Both hate the Shining Path for its 1980s terrorist rampage that killed tens of thousands of civilians. Peruvian police captured its founder, Abimael Guzmán, in 1992, and the group’s capacity to inflict harm greatly diminished. Today the Shining Path is a big-time drug trafficker and still practices political terrorism.

In his July 28 inaugural address, Mr. Castillo emphasized his determination to rewrite the constitution. He claims to be a democrat. Yet nearly 8 in 10 Peruvians in a Datum poll released in mid-June said they oppose a new constitution. Mr. Castillo’s proposal to have a new Magna Carta drawn up anyway, by an assembly that includes activists chosen by particular social, political and ethnic groups, is pure fascism.

One risk seems clear: With enough legal backing, control of the coca-growing regions, a paramilitary acting as his local enforcer, and command of the army, Mr. Castillo could easily copy the model used by Bolivia’s Evo Morales to build a narco-state and stay in power indefinitely. But Mr. Castillo’s Shining Path links suggest something more extreme in the making.

The day after the inauguration, Mr. Castillo stunned the nation by naming Shining Path aficionado Guido Bellido prime minister. The 42-year-old Cuzco native is an admirer of the Cuban regime, which he says is not a dictatorship. He also is close to Perú Libre’s founder, Vladimir Cerrón. Mr. Cerrón is a hard-core communist who lived in Cuba for 10 years and wants to remake Peru into a one-party socialist paradise like Venezuela.

Some have speculated that in naming Mr. Bedillo, Mr. Castillo made a miscalculation, which he regrets. His quick decision to name the left-wing, but reportedly moderate, Pedro Francke as his finance minister is supposed to be proof of his contrition.

This is naive. The appointment of Mr. Francke, a former World Bank economist, may imply moderation. But putting him in the cabinet is lipstick on a pig. Religion is being used in a similar way to convince social conservatives in rural areas that the Castillo crowd is virtuous. I still remember a Hugo Chávez planning minister—a University of Chicago-trained economist—who told journalists that to criticize the economy was “a sin against the Holy Spirit.”

Mr. Castillo’s effort to calm markets with the appointment of Mr. Francke hasn’t worked. Capital is fleeing the country. Reuters reported last week that stocks were trading at eight-month lows and the sol, Peru’s currency, was trading near all-time lows.

Markets are spooked, as are Peruvians, for good reason: The president is trying to provoke a constitutional crisis that would allow him to seize power.

The 1993 constitution allows the executive to close Congress if it gives him two votes of no confidence. By law Congress is supposed to approve his new cabinet. So he’s populated his list of nominations with extremists, Shining Path sympathizers and even one former terrorist who served in the left-wing military dictatorship of Juan Francisco Velasco Alvarado. Mr. Castillo is daring Congress to defy him. After the second time he can send them home.

If Congress is closed, there must be an election within four months. In the interim the president is supposed to have only emergency powers. But in practice, due to precedent set by former President Martín Vizcarra, Mr. Castillo is likely to rule by decree.

Legally he cannot initiate the process to rewrite the constitution without congressional approval. But Mr. Castillo’s radicalism raises questions of whether, short of the military stepping in to uphold its oath to the constitution, he could be stopped.

On Thursday a Perú Libre congressman taunted his opponents in the chamber to trigger its closure. Such incivility could backfire. Congress can vote to impeach Mr. Castillo, and later his militant vice president, with 87 votes out of 137. Both impeachments would be legal, ethical and, because Mr. Castillo shows no interest in governing democratically, may be the only way to escape the imposition of a new tyranny.

Write to O’Grady@wsj.com.

Journal Editorial Report: The week's best and worst from Kim Strassel, Mene Ukueberuwa and Dan Henninger. Images: AFP/Getty Images Composite: Mark Kelly The Wall Street Journal Interactive Edition