WASHINGTON/TOKYO -- When dovish, soft-spoken Fumio Kishida became Japan's 100th prime minister in October 2021, a briefing paper for U.S. President Joe Biden focused on two characteristics: "competence" and "caution."

U.S. President Joe Biden, right, with Japanese Prime Minister Fumio Kishida at the White House in January 2023: Both are suddenly signaling their imminent departure from office, fueling uncertainty over their successors. (Pool via Reuters)
Uncertainty over successors threatens momentum of 'global partnership'