In the coming weeks, the focus of presidential election politics is set to be put on who will emerge as the unified candidate of the liberal opposition camp. Discourse is heating up on how to establish the single candidacy between Rep. Moon Jae-in of the main opposition Democratic United Party and software mogul-turned-professor Ahn Cheol-soo.

Moon, a human rights lawyer and former chief of staff for late President Roh Moo-hyun, was nominated as DUP presidential candidate Sunday as he secured more than half the votes cast in the 13 regional primaries with his victory in the final contest in Seoul. Ahn, dean of the Graduate School of Convergence Science and Technology at Seoul National University, is expected to announce his presidential bid this week.

Ahn, who said last week he would make public his stance soon after the nomination of the DUP candidate, visited a cemetery honoring those killed in the 1980 Gwangju pro-democracy uprising on Friday in a move that political observers interpreted as signaling he would run in the presidential race.

Both sides have expressed the need to present a united front against Rep. Park Geun-hye, who was nominated by the conservative ruling Saenuri Party as its candidate for the Dec. 19 presidential election. A recent survey showed Park leading both Moon and Ahn by comfortable margins in a hypothetical multi-way race, with the gaps being closely narrowed in match-ups between the Saenuri contender and either of her two liberal rivals.

Moon and Ahn have also seen Park’s approval rating slip recently after her controversial remarks about the authoritarian rule of her father, President Park Chung-hee who ruled the country for 18 years until he was assassinated by his intelligence chief in 1979.

A tug of war is expected to be staged between Moon and Ahn for the weeks to come over how to unify their candidacy.

At the moment, none of them seems to make an easy concession. Riding on a string of wins in the DUP primary race, Moon beat Ahn for the first time in their approval rating as a single opposition candidate in a poll conducted early last week.

Many figures in the liberal camp are concerned that the prolonged confrontation over the concrete ways of unifying the candidacy might strain the relationship between Moon and Ahn, hampering the prospect of winning back power from the conservative bloc. It is likely that calls will be mounting for a one-on-one meeting between them to decide who will become the single candidate.

For a certain period of time, Moon and Ahn are expected to focus on expanding their support base, building pressure on each other to make concessions.

Moon is tasked with healing the intraparty rift that has widened in the course of primary contests and shedding his image tied to the legacy of Roh, which has been shunned by moderates. Ahn, who is popular with younger voters for his clean and upright image, will have to go through a toughening process of verifying his past records and qualifications as national leader.

The single candidacy would enable either of them to pose a formidable challenge against the Saenuri candidate. But the key to achieving their eventual political goal will be convincing voters of their ability to handle the complicated problems the nation faces.