Midway through last year, when Pedro Castillo began pulling into the lead in Peru’s presidential runoff election, Brazil’s Jair Bolsonaro reacted in the least diplomatic way possible. “We’ve lost Peru. It’s going to be the guy from the [transnational left-wing group] São Paulo Forum,” he said. But diplomacy under Mr. Bolsonaro is filled with surprises. The far-right leader and his far-left counterpart left their ideological differences aside during their first in-person meeting on Thursday — agreeing to a common agenda to strengthen economic ties.
In the first bilateral meeting between both countries’ heads of state in nine years, Messrs. Bolsonaro and Castillo agreed to create a working group...