IT is inconceivable that J. Edgar Hoover would ever have investigated members of Congress to gather evidence for possible prosecution. Hoover’s FBI learned a great deal about congressmen, and may have gone out of its way to collect more information than it needed, but all this would have been locked discreetly away, or possibly leaked, most privately, to a President or attorney general whose taste for gossip Hoover wished to gratify or whose personal loyalty he wished to assure.  The Bureau’s shrewd cultivation of congressional and White House opinion, effective for decades, was in time denounced as evidence that the FBI was “out of control,” immune from effective oversight.