In a local race with national implications, next month’s Yokohama mayoral campaign has suddenly become a major challenge to Prime Minister Yoshide Suga on his own turf and a threat to the ruling coalition's backing of a controversial casino resort plan.

Last month, Hachiro Okonogi, 56, a Liberal Democratic Party Lower House member, announced he would enter the race as an opponent of the plan, which Suga supports. That move means the anti-resort vote could be further split, as Constitutional Democratic Party of Japan-backed Takeharu Yamanaka, 48, and former Nagano Gov. Yasuo Tanaka, 65, are also running against the project.

Suga, still dealing with the failure of the LDP and Komeito to secure a majority in Sunday's Tokyo Metropolitan Assembly election, now faces the prospect of seeing Okonogi, an old ally and son of the prime minister’s political mentor, become mayor and scuttle the Yokohama casino plan.