South Korea’s presidential race was upended Thursday, less than five weeks until election day, when the front-runner was ordered to undergo a new trial on charges of election law violations and the nation’s acting president resigned amid speculation he will enter the field.

South Korea’s acting leader, Prime Minister Han Duck-soo, says he is resigning amid reports he will run in next month’s presidential election.

Prime Minister Han Duck-soo has been mulling whether to contest the election, while the main opposition candidate and front-runner suffered a setback in court.