It’s no small irony that Abimael Guzmán—the Maoist revolutionary who founded the Peruvian terrorist organization Shining Path some 50 years ago and died on Sept. 11—lived just long enough to see a Marxist-Leninist, Pedro Castillo, assume Peru’s presidency.

Although Guzmán and most Shining Path members gave up armed terror after his capture in 1992, his acolytes—represented today in both Mr. Castillo’s cabinet and the Peruvian Congress—never gave up their quest for power. Mr. Castillo is pushing for a new constitution that would concentrate political and economic power in the government and has appointed a prime minister who is a longtime Shining Path sympathizer—moves that already are undermining social cohesion and confidence in the economy and are likely to affect private investment. It’s not encouraging.

In 1989 and 1990, as a young activist in my father’s presidential campaign, I accompanied him to the funerals of some of the more than 100 members of his Freedom Movement party, most of whom were poor, who had been killed by Shining Path.