J.Edgar Hoover's Kahane obsession?

Forward reports that the late FBI boss, J.Edgar Hoover, had an obsession with the now defunct Jewish Defence League's and Kach's late leader Meir Kahane.

Kahane, an Orthodox rabbi in Brooklyn and the JDL's national chairman, was closely monitored as a "priority 1" on the bureau's security index. The FBI was especially concerned about the JDL's harassment and potential attacks on Soviet diplomats and installations at a time when President Nixon and his national security adviser, Henry Kissinger, were promoting "détente" with Moscow. In early 1971, Hoover regularly sent "priority" memos on Kahane to Kissinger, Secretary of State William Rogers, CIA Director Richard Helms, Attorney General John Mitchell and the head of the secret service.

An irony here is that Kahane claimed (back in 1972) to have worked for the FBI as a spy on another racist organisation: the John Birch Society. This must have been during Hoover's stewardship of the FBI.