His angry letter prompted close scrutiny of his political views and associations by the bureau that ran on into the early 1970s. The suspicion was that Seeger, who died in early 2014, was a security risk with close connections to the Communist party.

The FBI file on him has nearly 1,800 pages – 90 of them are still withheld for security reasons – and journalist David Corn has unearthed details within it of the elaborate efforts made by government agents to document Seeger’s activities, even back to his school days.