Richard Nixon resigned the presidency on August 9th, 1974. He was succeeded by his appointed Vice President, Gerald Ford. On September 8th, 1974 Ford granted Nixon a "free and full" pardon.
The US President has the authority to grant pardons to federal judges for anything except impeachment. There is no pardon from impeachment.
impeachment
The president of the United States is not allowed to grant pardons in cases of impeachment. The president can grant pardons in other cases though.
The US President can pardon any violation of federal law. He cannot use the pardon, however, to reverse a conviction that follows impeachment of an official. And he cannot extend a pardon to crimes that have not yet been committed.
The President is explicitly prohibited from pardoning someone who has been found guilty in an impeachment trial.
By appointing Article III federal judges to the Judicial Branch, and by granting pardons (may not grant a pardon for an impeachment).
The president has the power to give a pardon with the help of other officials. The president has the power to give a pardon with the help of other officials.
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The president may not grant a pardon in a case of impeachment. This means that he cannot allow a US official to escape removal from office if convicted by the Senate in the impeachment process. The President may still grant a pardon for the underlying criminal action for which the official is impeached so that that official cannot be punished for the criminal offense. But even if that official is pardoned for that criminal offense, he/she may still be impeached and removed from office because of it.
Pardons
As the majority consensus is that a President can pardon himself, he could theoretically get away with it. However, he would have to pardon himself before an impeachment. Given that, it's a bit silly, as it would be easier for the VP to simply have someone else do it, then pardon the someone else. Of course, what could be done once could be done twice. So it's unlikely that even an evil VP would wish to set that precedent, or it would be round after round of murder and pardon.
No US President is charged with impeachment at this time! The last President to face impeachment charges was Bill Clinton.