Election offices are sent envelopes with fentanyl or other substances. Authorities are investigating

Emergency and law enforcement agencies respond to a possible hazmat situation at the King County Elections office Wednesday in Renton, Wash. Four county elections offices in Washington state were evacuated Wednesday after they received envelopes containing suspicious powders — including two that field-tested positive for fentanyl — while workers were processing ballots from Tuesday’s election. (Karen Ducey/The Seattle Times via AP)

WASHINGTON— Authorities on Thursday were trying to determine who sent suspicious letters, including some containing fentanyl or other substances, to local election offices, attacks that appear to have targeted multiple states in the latest instance of threats faced by election workers around the country.