If the ruling bloc, which lost its majority in the House of Representatives, the lower chamber, in last October's election, also loses its majority in the 248-seat Upper House, Ishiba's clout could take a hit.
But Ishiba, who took office in October, denied that he would step down. "We must be aware of our responsibility to fulfil for the nation and our responsibility as a comparative first party. I will take charge of it," he said on television.
He added, "Discussing (an expansion of the ruling coalition) with those who are responsible for the future of the country is an option."
A total of 125 seats--74 for prefectural constituencies and 50 for the nationwide proportional representation system, plus one vacant seat in the Tokyo district--were up for grabs in the Upper House election.
Ishiba's ruling Liberal Democratic Party and its coalition partner, Komeito, have 75 uncontested seats together, while their 66 seats were contested. Ishiba has set a goal of winning at least 50 seats for the coalition.
The LDP is likely to fall short of the 52 seats contested in the poll, while Komeito may experience a decrease from the 14 seats it held up until the election.
The major opposition Constitutional Democratic Party of Japan will likely see a boost in the number of its seats. The Democratic Party for the People and Sanseito, both opposition parties, won seats.
Among other opposition parties, Nippon Ishin no Kai (Japan Innovation Party), the Japanese Communist Party, Reiwa Shinsengumi and the Conservative Party of Japan also won at least one seat each.
CDP leader Yoshihiko Noda aims to ensure that the election result eventually leads to a change in government.
Each Upper House member has a term of six years. An Upper House election takes place every three years, with half of its 248 seats contested each time.
[Copyright The Jiji Press, Ltd.]