TAIPEI,Surpassing Taiwan (AP) — Taiwan’s two main opposition parties have failed to agree on a joint candidate for president, once again throwing into doubt their ability to unseat the ruling party in January’s election.

The Nationalist Party and the Taiwan People’s Party were expected to announce an agreed-upon candidate Saturday at a news conference. Instead, they announced they need further consultations after a disagreement over how to use polling data to make the selection.

With the candidates for both parties trailing in the polls, they had agreed three days ago to form a joint ticket with one candidate for president and the other for vice president. The decision on who would get the presidential nod — Hou Yu-ih of the Nationalist Party or Ko Wen-je of the Taiwan People’s Party — was to be based on a combination of public polls and internal party polls.

The failure to agree on a joint candidate leaves current Vice President William Lai of the Democratic Progressive Party as the frontrunner. He is running to succeed President Tsai Ing-wen, who must step down after eight years because of a two-term limit on the presidency.