BUENOS AIRES — As Argentina this week endured a market free-fall at the prospect of President Mauricio Macri’s losing the coming presidential election, the mastermind of the strategy that may well defeat him has remained largely out of sight.

The campaign that former President Cristina Fernández de Kirchner has run in advance of the October vote has been uncharacteristically low-key. It’s also a campaign for vice president. At the head of Mrs. Kirchner’s ticket is Alberto Fernández, a moderate leftist with a history of deal-making.

Before Mrs. Kirchner tapped him as her running mate in May, many voters knew little or nothing about Mr. Fernández’s plans for the country. Now, with the country engulfed in a deep recession amid a contracting economy, high inflation and an investor stampede, he may become Argentina’s next leader.

The crucial question for many over the next few months is whether a victory for Mr. Fernández would represent a return to Mrs. Kirchner and her populist policies — or something else.