The Trump administration discusses the possibility of pardoning Donald Trump, his family, and loyal members of the administration for crimes that they have not been charged for. Can the president even do such a thing, or must they wait for the charges to be filed?
In Ex parte Garland, 71 U.S. (4 Wall.) 333 (1866), the Supreme Court ruled on the limitations of the presidential pardon:
153 The Constitution provides that the President 'shall have power to grant reprieves and pardons for offences against the United States, except in cases of impeachment.'
154 The power thus conferred is unlimited, with the exception stated. It extends to every offence known to the law, and may be exercised at any time after its commission, either before legal proceedings are taken, or during their pendency, or after conviction and judgment. This power of the President is not subject to legislative control. Congress can neither limit the effect of his pardon, nor exclude from its exercise any class of offenders. The benign prerogative of mercy reposed in him cannot be fettered by any legislative restrictions.
This means that the pardon can only be used to pardon offences that have already been committed, even if the offender has yet to be charged with a criminal offence. In this sense, the pardon can be used preemptively, but not in the sense that the pardon could be used to preemptively pardon an offence that has yet to be committed.
With regard to the implied question of whether a President may pardon themselves for their own crimes, I refer you to the answer given here, but in short, maybe; there is no explicit restriction in the Constitution or Supreme Court decision, and this has never been tested, however it seems likely that it would be challenged judicially.
As Rick Smith pointed out in a comment, possibly the most famous example of such a preemptive pardon was when President Gerald Ford pardoned President Richard Nixon after the latter resigned as a result of the Watergate scandal. Proclamation 4311 states:
I, Gerald R. Ford, President of the United States, pursuant to the pardon power conferred upon me by Article II, Section 2, of the Constitution, have granted and by these presents do grant a full, free, and absolute pardon unto Richard 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.
As you can see, the pardon was not specific about which offenses were being pardoned, but rather granted a blanket pardon of all potential offenses which Nixon may have been guilty of during his tenure as President. Nixon was not required to be formally charged with any offenses in order to receive this pardon.