In 1930, it was Wobblies.
In 1957, it was fellow travelers.
In 1971, it was insane telepaths.
And, in 1973:
“We don’t know what the hell it is,” said Andrew J. Burris, Director of the FBI. He threw his hands in the air and looked baffled and confused.
Kenneth J. Malone tried to appear sympathetic. “What what is?” he asked.
Burris frowned and drummed his fingers on his big desk. “Malone,” he said, “make sense. And don’t stutter.”
“Stutter?” Malone said. “You said you didn’t know what it was. What the hell it was. And I wanted to know what it was.”
“That’s just it,” Burris said. “I don’t know.”
Malone sighed and repressed an impulse to scream. “Now wait a minute, Chief—” he started.