The “misconduct” was revealed by White House Counsel John Dean (under questioning in the Senate Watergate Hearings) that White House operatives had broken into Ellsberg’s psychiatrist’s office as part of a plan to blackmail Ellsberg. Nixon Special Counsel Charles Colson went to prison for his involvement in the break-in.
Ellsberg worked on the Top Secret McNamara study of U.S. Decision-making in Vietnam, 1945-68, which later came to be known as the Pentagon Papers. In 1969, he photocopied the 7,000 page study and gave it to the Senate Foreign Relations Committee; in 1971 he gave it to the New York Times, Washington Post and 17 other newspapers. Before the dismissal, he faced twelve felony counts posing a possible sentence of 115 years. The events led to the convictions of several White House aides and figured in the impeachment proceedings against President Nixon.
A few years ago, Pat Buchanan blamed (credited?) Ellsberg for America’s loss in Vietnam.
Thanks to Jack Dean for pointing this out.