Western officials are investigating whether devices planted at shipping hubs in Europe may have been a test run by Russian operatives for placing them on planes bound for the U.S.
Intelligence officials said that foreign adversaries were planning to take advantage of another close U.S. election to undermine trust in the country’s democratic process.
Some current and former officials have said the 2019 F.B.I. analysis sowed doubt within the C.I.A. and parts of the Trump administration about the root causes of the ailments.