The world's biggest pension may find that when it comes to returns on its $1.3 trillion in assets, Donald Trump giveth and taketh away.

What started as a rally in stocks on his presidential victory five months ago turned into a slump this year, making it harder for Japan's Government Pension Investment Fund to beat its record $92 billion gain in the fourth quarter, according to SMBC Nikko Securities Inc. and BNP Paribas Securities Ltd. in Tokyo. GPIF may announce that assets shrank by about ¥300 billion ($2.7 billion) when it reports first-quarter results in July, BNP Paribas said.

A loss for the retirement fund would take some of the shine off two consecutive quarterly gains that were mainly driven by foreign and domestic stocks, while Japanese bonds declined. The Topix has erased its year-to-date advance as the yen surged amid speculation U.S. tax reform would be delayed after Republicans abandoned efforts to repeal and partially replace Obamacare.