With Naoto Kan announcing in October that he will not run in the next general election, the Constitutional Democratic Party of Japan (CDP) — the main opposition party — will lose a high-profile figure and political veteran from the party’s liberal wing.

“I am trying to make arrangements on how to officially decide on a successor, but would like to resolutely hand over the banner of 'civic politics' and the liberal fight to the younger generation,” the former prime minister wrote on X, formerly Twitter.

But that may be easier said than done, as the party's main support group, Rengo (Japan's largest labor organization), appears to be moving closer to the ruling Liberal Democratic Party, while CDP cooperation with the Japanese Communist Party at election time may not inspire a groundswell of support among the younger generations.

Early in his career, Kan was seen as a symbol of liberal, civil society politics — though his public profile has declined in recent years. As health minister in Prime Minister Ryutaro Hashimoto’s Cabinet in 1996, Kan unearthed missing ministry documents proving the connection between contaminated blood products and hemophilia patients who had contracted HIV, apologizing and admitting the government’s responsibility in the scandal.

Kan served as prime minister between June 2010 and September 2011, as head of the now-defunct Democratic Party of Japan. He led the nation at the time of the March 11, 2011, Great East Japan Earthquake and tsunami, and the triple meltdown at the Fukushima No. 1 nuclear power plant that followed, becoming a staunch opponent of nuclear power. He stepped down due to widespread criticism of his handling of the disaster. Kan was replaced by Yoshihiko Noda, another former DPJ member who is also now with the CDP.

CDP leader Kenta Izumi said he spoke to Kan about his decision to retire from politics.

“Kan told me: 'I've been talking about generational change for a long time, and I have high expectations for the younger generation,'” Izumi wrote on X.

Kan and Izumi have a complicated relationship. In the November 2021 CDP presidential election, Kan supported Chinami Nishimura (currently the party’s deputy president) who is a member of Kan’s group of more liberal CDP members. But the more conservative Izumi won the election with the backing of CDP members like veteran political heavyweight Ichiro Ozawa.

Ozawa was once one of most powerful members of the LDP before joining the opposition forces. He played a key role in helping the DPJ defeat the LDP in 2009.

Kan’s announcement came the day before a Lower House by-election in Nagasaki Prefecture and an Upper House by-election in Shikoku for the Tokushima-Kochi district. The LDP held both seats prior to the contests. But in the Upper House race, opposition-backed independent Hajime Hirota, a former CDP Lower House lawmaker, defeated LDP-Komeito candidate Ken Nishiuchi.

In the Nagasaki Lower House by-election, however, CDP candidate Seiichi Suetsugu — who was supported by the Social Democratic Party of Japan, and endorsed by the JCP and Democratic Party for the People – ended up losing to Yozo Kaneko, the ruling coalition pick. The margin of defeat was only around 7,000 votes, giving rise to questions about whether the CDP and other opposition parties, especially the JCP, can effectively cooperate on candidates in other districts once a general election is held. With Kan not running in the next general election, the Tokyo 18th district seat, which he has held since 1996, is up for grabs as well, but the CDP may insist on one of its members running there.

Although the CDP is talking about generational change with Kan’s exit, Ritsumeikan University political scientist Masato Kamikubo said the move is unlikely to have a large impact on the party.

“Kan's retirement will not affect the CDP," he said. "He was already something of a neglected figure, not only within the CDP but also in the political world as a whole.”

Rather, he added, Kan’s announcement reflects a shift of power already underway between the CDP and Rengo.

Kan’s close relations with Rengo had been passed on to one of his disciples, former CDP president Yukio Edano. But after Edano resigned in November 2021 due to the party's poor performance during the Oct. 31 Lower House election, the CDP-Rengo relationship began to weaken.

While Edano is reportedly eyeing a return to the presidency prior to the by-elections, Rengo has been talking to the ruling LDP-Komeito coalition more since Edano stepped down, in order to press the coalition over issues directly affecting its members.

“Kan's retirement may symbolize the trend of Rengo moving closer to the LDP, and the LDP-Rengo relationship, (which is mostly focused on) wage increases, may strengthen,” Kamikubo said.

The CDP has hinted at a tie-up with the JCP in the next general election to field unified candidates, despite the fact that in some regions, CDP supporters remain opposed to cooperation with the JCP. Rengo, meanwhile, will not officially support any candidates that have JCP backing.

That could spell trouble at the polls for a CDP leadership hoping a unified candidate will appeal in particular to younger, more left-leaning voters.

“Many of Kan's supporters are left-wing civil society activists. But it’s possible they're disappointed with the JCP and could shift their support to other more left-wing parties, such as the Reiwa Shinsen Gumi," Kamikubo said. "The number of people, especially young civic activists, supporting the JCP-CDP joint struggle will sharply decline, as they have no hope for the JCP’s future.”