New Delhi, Sept. 8 -- Argentine President Javier Milei suffered a sweeping setback on Sunday in a Buenos Aires provincial election widely viewed as a political test for his libertarian party and a barometer for how it will perform in crucial congressional midterms next month.

Milei's recently formed La Libertad Avanza party captured just 34% of the vote in Argentina's biggest province, losing by a landslide to the left-leaning Peronist opposition, which secured 47% with the majority of ballots counted late Sunday.

Milei conceded that his right-wing party's crushing 13-point loss to his populist rivals represented "a clear defeat."

"We suffered a setback, and we must accept it responsibly," Milei told grim-faced supporters at the party ...