The outcome of Japan's ruling party leadership race, which will choose the successor to Prime Minister Yoshihide Suga, has become more difficult to anticipate now that four senior lawmakers have entered the race, raising the possibility of a runoff.

But one thing is certain: Liberal Democratic Party lawmakers are under greater pressure to heed public opinion on who should succeed Suga than play by faction rules.

The term of House of Representatives members expires on Oct. 21, meaning that whoever wins the most votes and becomes the new LDP president — and hence prime minister — will lead the party and its coalition partner Komeito into a general election in the fall.