Despite being such a broad and unique power, presidential pardons do have limitations.
Any elected and appointed official of the United States is subject to removal from office by impeachment [Source: University of Missouri-Kansas City]. With a simple majority (50 percent of the vote, plus one extra vote) the House of Representatives can impeach an official, and the article of impeachment is sent to the senate. In the Senate, the decision to remove the impeached official from office is made with a two-thirds vote.
The Constitutional framers chose to allow impeachment proceedings not just for those holding office, but for officials who have previously held office. This second method of impeachment results in the former official being banned from holding any office again.
The impeachment process is excluded from the scope of the president's pardon power because the president can also be impeached. A discussion by the framers over the potential for the executive gaining absolute power was resolved by the threat of impeachment. The framers reasoned that if the president knew he could be impeached, and if impeachment was outside of his pardon power, then this should keep the president from getting too powerful.
The exclusion of impeachment from the scope of pardons was included in the wording regarding pardons in the Constitution. Over the course of more than two centuries, the power of the pardon has been further limited by federal court cases. While the Supreme Court has generally erred on the side of the Constitution in cases where the pardon power has been challenged, the court has also further defined the power to pardon through a series of cases.
One limitation is that a pardon cannot be issued for a crime that has not yet been committed. Pardons also don't affect civil cases, or state or local cases. Pardons are meant to dismiss sentences stemming from affronts to the United States through the breaking of laws. They're not intended to relieve an individual from his responsibility to make restitution to a victim's family, for example, which would be considered a personal affront. So a presidential pardon of a criminal sentence would not relieve the defendant from paying restitution from a related civil case.
Pardons also don't work unless the person to whom the pardon is granted accepts the pardon. A 1915 Supreme Court case decide that it was to be left up to the grantee of the pardon to decided whether he wants to accept the pardon or not. This seems self-evident, but some federal cases have challenged this once hard-and-fast rule. In one, the Supreme Court decided that matters of life and death fell outside this ideal.
It was decided that if a president decided to commute a prisoner's sentence from the death penalty to life in prison, the prisoner had no choice in the matter. President Calvin Coolidge further deconstructed this rule. When a prisoner he had granted a pardon to refused it, Coolidge told the warden to remove the prisoner and "lock the doors behind him" [Source: USConstitution.net].
When it was established that the pardon is to be used solely to grant reprieve from affronts committed against the United States, a loophole was opened. Pardons have been demonstrated to not legally have an effect on contempt of court charges since, like a civil case, a contempt charge isn't considered an affront to the United States; instead, it's considered an affront to the court.
This caveat also provides Congress with a way to get around the presidential pardon. This resulted in the relatively modern concept of the pardon and its use as a political tool. Check out the next page to learn about how the modern pardon has become a double-edged sword for Congress and the executive branch.