Japanese Prime Minister Shigeru Ishiba will announce his resignation by the end of next month, Japanese media reported on Wednesday, following a bruising election defeat that cost his administration its upper house majority.

The reports come after Ishiba and US President Donald Trump unveiled a trade deal that lowers tariffs on imports of Japanese autos and spares Tokyo punishing new levies on other goods.

In the wake of Sunday’s poll drubbing, Ishiba said he would stay in office to pursue the tariff agreement and tackle mounting economic problems.

“I can’t say until I scrutinise the outcome of the agreement,” Ishiba told reporters on Wednesday when asked whether the tariff deal with Washington would influence his decision on whether to stay on.

Ishiba told his close associates on Tuesday evening that he would address his responsibility for the election loss after a trade deal had been reached, the Yomiuri newspaper reported earlier.

His departure less than a year after taking office would trigger a succession battle within the ruling Liberal Democratic party as it contends with challenges from new political parties, particularly on the right, that are stealing its support.

Among them is the “Japanese First” Sanseito far-right group which surged in Sunday’s vote, growing its representation in the 248-seat upper house to 14 from one. The party has attracted voters with pledges to curb immigration, slash taxes, and provide financial relief to households squeezed by rising prices.

Ishiba defeated hardline conservative Sanae Takaichi in a party leadership runoff last year.

Ishiba is expected to meet ruling party heavyweights later on Wednesday for discussions on the election outcome.