It all started when the White House decided it didn't like Schorr's reporting on the CBS Evening News. As Schorr told NPR's Terry Gross in a 1994 (rebroadcast on July 30, a week after Schorr's death; the transcript is here, and you check it out on iTunes here):
[Nixon] had Haldeman have his assistant Larry Higby call J. Edgar Hoover and simply say the boss, the president, wants to have some background stuff on a correspondent named Daniel Schorr.But either Higby or the FBI's usually pretty canny director missed the point. Rather than dishing whatever dirt happened to be on hand, Hoover ordered a full field investigation, the kind the FBI does on those in line for high-level government jobs. When agents visited Schorr himself, inadvertently revealing that the White House and a federal police agency had developed a constitutionally unhealthful fixation on him, Nixon aides concocted the story that they were planning to offer one of Washington's most prominent journalists the lofty post of PR man for the Council on Environmental Quality.
This bumptious episode turned deadly serious, Schorr told Gross, when the use of the FBI against a journalist was cited by the House Judiciary Committee in one of the three articles of impeachment it approved in the summer of 1974.
Admiring Nixon for his final comeback, Schorr became a regular guest at Nixon Center events in Washington during the 1990s. At one, the ex-president smiled at him and said, "Damn near hired you once." To Gross's apparent surprise, Schorr chose to take Nixon's remark as a backhanded apology. "[Only] he who is without blemish should be casting stones around," Schorr said. "I consider life too short to have grudges, retain grudges, and furthermore, I find him interesting."