Q: Can a president issue a blanket pardon to an individual for crimes that may have been committed in the past but have not yet been discovered?
A: Yes. That’s just what Gerald Ford did when he granted "a full, free, and absolute pardon" to Richard Nixon for crimes he "has committed or may have committed" while in office.
Ford granted the blanket pardon to former president Nixon on Sept. 8, 1974, a month after Nixon had resigned from office in the wake of the Watergate scandal.
Nixon faced certain impeachment by the House and probable conviction and removal from office by the Senate as a result of evidence showing that he had ordered a criminal cover-up of the role of White House and campaign operatives in the illegal wiretapping of Democratic National Committee headquarters. Tape recordings of Nixon’s conversations that took place in the Oval Office just days after burglars were arrested inside DNC offices on June 17, 1972, showed that the president knew his own attorney general, John Mitchell, and other subordinates were involved and that he ordered the FBI to halt its investigation on spurious national security grounds.
Ford’s pardon ended any possibility of Nixon being prosecuted criminally. It covered more than obstruction of justice, however. It excused Nixon for "all offenses against the United States which he, Richard Nixon, has committed or may have committed or taken part in" during the period from January 20, 1969, through August 9, 1974. In short, Ford’s pardon covered any crimes Nixon may have committed between the time he was sworn in for his first term and the day he resigned.
The full text of the pardon can be seen at the Web site of the Gerald R. Ford Library and Museum. An image of the actual document may be viewed at the Watergate.info Web site, which is the project of an Australian teacher.