The FBI has misused a powerful digital surveillance tool more than 278,000 times, including against crime victims, Jan. 6 riot suspects, people arrested at protests after the police killing of George Floyd in 2020 and — in one case — 19,000 donors to a congressional candidate, according to a newly unsealed court document.

FBI officials say they have already fixed the problems, which the agency blamed on a misunderstanding between its employees and Justice Department lawyers about how to properly use a vast database named for the legal statute that created it, Section 702 of the Foreign Intelligence Surveillance Act (FISA).