New Prime Minister Shigeru Ishiba to stay on in Tokyo, playing a weaker hand

SEOUL, South Korea — Did Shigeru Ishiba push the risk too far?

Gambling in a bid for a stronger mandate, Japan’s new prime minister called a general election a year before he needed to, only to see his Liberal Democratic Party and its coalition partner lose their comfortable majority in the Diet’s Lower House in Sunday’s vote. The result raises fresh questions about the staying power of a key U.S. ally in Asia.

Mr. Ishiba made clear on Monday that he will stay on, even if his ability to enact legislation has been weakened.

“I want to continue to carry out my duties,” he told reporters in Tokyo. “I will tackle the current severe challenges.”

Mr. Ishiba, a veteran power in the conservative LDP, became prime minister in September after sitting Premier Fumio Kishida decided not to run.

Instead of securing a freer hand to govern, Mr. Ishiba now must court minority parties and possibly hold his nose and welcome back ex-LDP lawmakers who were booted from the party in a corruption scandal but will sit in the next parliament as independents.

At worst, Mr. Ishiba may face challenges from within his party and suffer the ignominious fate of his two predecessors: Neither prime minister completed a full term in office, and both were pressured to step down due to their unpopularity.

At a time when Tokyo faces delicate issues both domestically and in a region where North Korea and China pose major challenges, analysts say a return to “revolving-door” prime ministers is the last thing Japan needs.

Sunday’s general election was called by Mr. Ishiba in hopes of securing a national leadership mandate and to distance himself from a long-lingering corruption scandal affecting the Liberal Democratic Party.

On Sunday, the LDP won 191 seats in the 465-seat Lower House. Its coalition partner, Buddhist Party Komeito, won 24. Combined the coalition controls 215 seats, 18 short of a majority, compared to the 297 seats the LDP-led coalition held before Sunday’s vote.

On paper, the ruling parties still hold a clear edge, but in practical terms, the loss of seats is a major blow to Mr. Ishiba’s month-old government.

The main opposition, the leftist Constitutional Democratic Party, won 148 seats — a sharp increase from their previous total of 98.

All is not lost for Mr. Ishiba: If he can garner the support of either one of the next two minority parties, he will reclaim majority control of the Lower House. The two likely sources: The populist right-wing Japan Innovation Party, or Nippon Ishin No Kai, which won 38 seats, and the broadly conservative Democratic Party for the People, which now has 28.

Mr. Ishiba hinted some dealmaking is in the country’s immediate future.

“There are parties that have greatly increased their parliamentary seats,” Mr. Ishiba said Monday.  “We have to look at what kind of arguments these parties made during the election and what resonated with the public.”

Another possibility is to lure ex-LDP lawmakers back into the fold.

Mr. Ishiba, a defense and security specialist, needs to move fast, as Japan is already bracing for the uncertain result of the coming U.S. presidential election next week. A victory for former President Donald Trump, the Republican presidential nominee, in particular could present several new challenges for the Ishiba government.

“Given that Japan is under the U.S. umbrella, [the Japanese] are also torn by what to do in a potential Trump world order,” said a person familiar with both American and Japanese affairs, on condition of anonymity. “Japanese news stations are hedging their bets. … They are terrified of what will happen if he wins.”

Both Japan and South Korea were shaken by Mr. Trump’s ambivalence toward alliances in his first term. His focus on obtaining higher payments from longtime allies in East Asia and Europe for overseas U.S. troop presences also shook many.

“Japan and Korea have too much to lose,” from the U.S. election, the source added.