The Liberal Democratic Party’s support fell 4.1 percentage points to 24% in a week, while backing for the LDP-led administration of prime minister Shigeru Ishiba stayed unchanged at 31%, in the poll taken between July 11 and 13.

LDP support has been falling in recent surveys, suggesting that Ishiba’s coalition of LDP and junior partner Komeito may lose its majority in the upper house too, after losing its lower house majority last October.

A poor showing would cast doubt on Ishiba’s political future as his shaky government faces an Aug 1 deadline to strike a trade deal with the US, less than two weeks after the vote.

The rise of smaller opposition parties that favour tax cuts and loose monetary policy could also complicate the Bank of Japan’s interest hike schedule.

In the latest NHK poll, the main opposition Constitutional Democratic Party received 7.8% support, slightly down from a week before, while Sanseito, which has been seen a dark-horse populist conservative group, rose to 5.9%.

Democratic Party for the People registered 4.9% support, LDP partner Komeito 3.5%, Japan Innovation Party 3.1% and Japanese Communist Party 3.0%, while 33.7% of respondents supported no party.