The revision of the Constitution is emerging as a top political issue ahead of the presidential election on May 9. How it evolves could affect the election in which a liberal is favored to win for now.

The move to amend the basic law has been expedited by the agreement of three major parties -- the Liberal Korea Party, the People’s Party and the Bareun Party -- to put their unified proposal to a referendum on the day of the presidential election.

The agreement, reached Wednesday by the three parties’ floor leaders and representatives to the parliamentary special committee on constitutional amendment, calls for the finalization of their proposal early next week.

Participants in the meeting said the proposal would be highlighted by changing the current five-year single term presidency to one in which the president is allowed to serve two four-year terms consecutively. Numerous opinion polls show that such a presidential system is most favored.

They also said the power structure under the proposal will be a sort of semi-presidential system, or dual executive system, in which the president is elected by a direct vote and the prime minister is selected by the parliament. The most common form is for the president to be responsible for foreign policy while the prime minister takes charge of domestic affairs.

These and other core elements of the proposal reflect well the view of the majority of the public that the current Constitution, last amended in 1987 in the wake of a pro-democracy movement, needs to be amended.

The agreement also came at the right time, as the impeachment of Park Geun-hye has been bolstering the call to curb the power of the president.

Constitutional Court Justice Ahn Chang-ho said that the 1987 Constitution -- which revived the direct, popular vote to elect the president, secured legitimacy for the presidential power but that it still allowed the president to remain as authoritarian as past dictators.

Such an “imperial presidency,” Ahn said in the verdict to oust Park, was a root cause of the influence-peddling and corruption scandal that led to her impeachment for abusing her power.

Despite the growing consensus, amending the Constitution according to the plan of the three parties would never be easy. The biggest hurdle is Moon Jae-in, the leading presidential hopeful, and his Democratic Party of Korea, as they insist that any revision should take place after the upcoming election.

Endorsement of Moon and the Democratic Party is crucial in that the combined number of parliamentary seats held by the three other parties falls short of the minimum two-thirds of the lawmakers -- 200 -- needed to earn a parliamentary approval, a step that should precede a referendum.

As expected, the party’s floor leader Woo Sang-ho called the three parties’ plan a “midsummer night’s dream,” saying that it would be impossible to get the proposal through the National Assembly without the consent of his party -- the largest, with 121 seats, of the five parties in the National Assembly.

There are some grounds for the party’s opposition -- the frontrunner Moon is highly favored to win power and the proposal also calls for the next president to shorten his term of office to three years so that the next presidential election to be held under the new Constitution coincides with the parliamentary election.

Granted, it would not be easy for anyone in Moon’s position to accept a proposal that could tamper with a presidency he sees now within reach. Moreover, Moon and his supporters see the proposal as a tactic by his opponents to form a united front against him.

But Moon’s insistence that the revision be made after election is not convincing either. Several presidents, including Park, promised to revise the Constitution if they were elected, but failed to keep their word. Besides, if Moon is elected and keeps his promise, it would not be desirable for a new president to spend precious time in the first year of his presidency on pushing the revision.

So it would be in the interests of all the parties and candidates -- and, more importantly, for the nation -- to reach a compromise before the election on when and how to revise the Constitution. It is needless to say that the No. 1 principle should be that the earlier the revision is made, the better it is for the nation.