LIMA, June 6 -- At a polling station in the Surco district of Lima, a retired schoolteacher named Olga Quispe said she had voted in every Peruvian presidential election since 1980. She had never, she said, felt less certain about what comes next. "Every time we think things will get better, someone else gets removed." Sunday's runoff - the tenth in the past decade that has produced a new head of state - will test whether that fatalism is warranted or whether Peru's democracy can finally stabilise.

The matchup is, on its surface, a familiar ideological split. Keiko Fujimori, the 50-year-old daughter of the late authoritarian president Alberto Fujimori, leads the conservative Fuerza Popular party and finished first in the April 12 first ro...