Japanese Prime Minister Shigeru Ishiba has vowed to remain in power to oversee the implementation of a new Japan-U.S. tariff agreement.

Shigeru Ishiba denied he had decided to quit after a source and media reports said he planned to announce his resignation to take responsibility for a bruising upper house election defeat.

The right-wing populist party Sanseito made big strides in parliamentary elections in Japan, capitalizing on concerns about the economy, immigration and overtourism.

The reports come after Trump announced a trade deal with Japan, and days after Ishiba’s governing coalition lost its majority in the country’s upper house.

As part of a trade deal reached this week, Japan agreed to invest $550 billion in projects across strategic U.S. industries, including energy, semiconductor manufacturing and shipbuilding. The White House said Trump would have final say over where the money goes and that the U.S. would keep 90% of profits on any investments.