New Delhi, July 19 -- Japan's Prime Minister Shigeru Ishiba faces an increasingly uphill battle in Sunday's upper house election, and a loss could worsen political instability at a time of daunting challenges, such as rising prices and high U.S. tariffs.

A poor performance would not immediately trigger a change of government but it would deepen uncertainty over his fate and Japan's future path.

The ruling Liberal Democratic Party suffered a humiliating loss in a lower house election in October as its usual supporters registered their unhappiness over past corruption scandals and high prices. Ishiba is struggling to regain voter confidence.

His minority government has since been forced into making concessions to the opposition to get le...