President Moon Jae-in has not made up his mind on whom to choose to replace Prime Minister Lee Nak-yon.

He was expected to announce Lee’s replacement in early December, when he nominated Choo Mi-ae, a five-term ruling party lawmaker, for the post of justice minister. But he stopped short of making public the candidate for the second prime minister of his administration.

Lee is believed to be hoping to return to the ruling Democratic Party to run in next April’s parliamentary elections as a springboard for a presidential bid.

If Lee, a former lawmaker and South Jeolla Province governor, wins in a hotly contested constituency, he can consolidate his foothold in the liberal ruling party.

Lee -- the longest-serving prime minister since the country introduced the current direct presidential election system in 1987 -- has topped the list of potential presidential candidates in recent opinion polls.

Moon seems to intend to help Lee with his future political course by relieving him of his administrative duties.

But the president has had difficulty finding a replacement who is both capable of handling thorny tasks -- particularly on the economic front -- and has support from his left-wing political base.

Until recently, Kim Jin-pyo, a four-term ruling party lawmaker, had been touted as a favorite for the post. Having worked as finance minister and deputy prime minister for economic affairs for two years from 2003, he could be a good choice at a time when the country is struggling to cope with deepening economic woes.

Kim also maintains relatively cordial relationships with conservative opposition lawmakers, which could help him win legislative support for measures needed to reinvigorate the economy.

Moon apparently considered him as his first choice to replace Lee, but balked in the face of vehement objections from progressive civic groups, labor organizations and ruling party legislators.

The main reason cited for opposing his selection was that he was an anti-reformist figure who had pushed for policies to promote corporate investment, including lowering tax rates levied on companies.

Moon should have surmounted such objections and picked Kim as his second prime minister if he was serious about carrying out his repeated pledges to strengthen support for corporate activity.

In recent months, he has said that achieving tangible economic results was his priority for the second half of his five-year tenure, which ends in 2022.

Such rhetoric will ring hollow if, out of concern about backlash from his support groups, he refrains from selecting a figure who can communicate smoothly with businesses as the next prime minister.

Moon now appears to be turning to Rep. Chung Sye-kyun, another ruling party heavyweight and a former National Assembly speaker, as a possible successor to Lee.

Last week, Chung suggested he may have been offered the job, telling a reporter, “I have yet to make up my mind.”

His experience as a corporate executive and industry minister may make him suitable for the post.

But in view of the principle of separation of powers among the administrative, legislative and judiciary branches, it is improper for him to be considered as a candidate for the No. 2 post in the administration.

His acceptance of Moon’s request to become his next prime minister would be seen as placing the legislature under the administration.

How awkward and shameful would it be for him to attend a parliamentary interpellation session on behalf of the president and answer questions from jeering lawmakers? As recently as last year, he overlooked the floor of the chamber from the speaker’s seat.

Moon is running out of time to choose a replacement for Lee if the latter hopes to pursue his political ambitions.

A public servant seeking to run in the April 15 elections must resign from his or her post no later than 90 days ahead of the voting date, which means he has until Jan. 15.

A few other ruling party lawmakers have been touted as noncontroversial but lackluster choices.

Moon needs to expand the scope of possible candidates and overcome objections from his support base if he wants a prime minister who can help him cope with economic woes and other challenges facing the nation.