Canada is heading toward a tight race in federal elections this month, with Prime Minister Justin Trudeau and his political rival, Conservative leader Andrew Scheer, sharing the lead in recent polls.

In a race this close, small details can sometimes cause big divisions.

And on Thursday, an uncomfortable fact about Scheer emerged: He’s also a U.S. citizen.

Scheer’s father was born in the United States, and Scheer and his siblings got U.S. passports as children, his campaign acknowledged after his dual citizenship was first reported by the Canadian newspaper the Globe and Mail. Speaking to reporters in Nova Scotia on Thursday, Scheer said he initiated the process to officially renounce his U.S. citizenship in August. His campaign also said he has not renewed his passport as an adult. But Scheer still struggled to explain why he had never publicly mentioned his dual nationalities before.