As the nation's ruling party prepares to select Prime Minister Shinzo Abe's successor, analysts in the United States are concerned that while they expect the U.S.-Japan alliance to remain robust, Tokyo may see a return to an era of revolving-door leadership amid a period of security challenges in Asia.

Chief Cabinet Secretary Yoshihide Suga is believed to be on course to win next Monday's ruling party leadership race that will decide the next prime minister, casting himself as a candidate qualified to carry Abe's policy legacy forward after serving as the administration's public face throughout its nearly eight-year span.

"Continuity is likely, and I think that's testament to Abe's influence and legacy," Michael Green, senior vice president for Asia at the Center for Strategic and International Studies, said at an online event, of the 65-year-old prime minister who doubles as Liberal Democratic Party president and announced in late August that he would leave halfway through his term due to a chronic illness.