Leftist Mexican President Andrés Manuel López Obrador—AMLO, as he is popularly known—has worked hard to convince markets that he is no Hugo Chávez. Former Argentine President Cristina Kirchner, maybe, but not Chávez.

Argentine politician Axel Kicillof fanned the flames of those fears when he visited Mexico earlier this month. A former economy minister for Mrs. Kirchner, Mr. Kicillof today calls himself a Keynesian. But while working in the Kirchner government he was known for hard-left antimarket activism and fiery rants...