A dozen years ago, John Mark Dougan, a former deputy sheriff in Palm Beach County, Fla., sent voters an email posing as a county commissioner, urging them to oppose the re-election of the county’s sheriff.

He later masqueraded online as a Russian tech worker with a pseudonym, BadVolf, to leak confidential information in violation of state law, fooling officials in Florida who thought they were dealing with a foreigner.

He also posed as a fictional New York City heiress he called Jessica, tricking an adviser to the Palm Beach County Sheriff’s Office into divulging improper conduct by the department.

“And boy, did he ever spill ALL of the beans,” Mr. Dougan said in a written response to questions for this article, in which he confirmed his role in these episodes.

Those subterfuges in the United States, it turned out, were only a prelude to a more prominent and potentially more ominous campaign of deception he has been conducting from Russia.

Mr. […]