Determining why a Boeing Co. passenger jet flown by China Eastern Airlines Corp. plummeted to the ground from 29,000 feet (8,840 meters) is a thorny task in itself. Now, politics risks complicating the investigation and amplifying the fallout.

With relations between Washington and Beijing at their lowest ebb in years, the probe into China’s worst aviation disaster in more than a decade — the crash of a U.S.-made plane run by a Chinese, state-owned airline — has turned the two archrivals into reluctant bedfellows.

Both sides stand to lose if the investigation becomes politicized, ensnared in a wider fight for dominance between the two superpowers that’s touched everything from trade and the origins of the coronavirus to the war in Ukraine.