Originally, however, a pardon could be refused. It is a part of the Constitutional scheme. When granted it is the determination of the ultimate authority that the public welfare will be better served by inflicting less than what the judgment fixed. A pardon can also be granted to a class of people, such as those involved in the Whiskey Rebellion. President James Carter pardoned all Vietnam draft dodgers.
Pardons can take place before or after a criminal proceeding.
President Gerald Ford, for example, pardoned Richard Nixon before Nixon was ever charged with, let alone convicted, of any crime. Such pardons, however, are rare, and general procedures dictate that at least five years of a sentence should be served before a pardon is considered. In the Constitutional Convention of 1787, this issue was brought up and debated quickly, with no restriction on when a pardon might be granted, suggested by James Wilson as a way of obtaining the testimony of accomplices. There are, however, things that a pardon cannot cover. The first and most obvious is impeachment, since it is specifically excepted in the Constitution.