On November 24, President Trump officially pardoned “Corn,” a 42-pound fowl dubbed the National Thanksgiving Turkey. But a U.S. president’s clemency powers extend far beyond ceremonial acts of mercy like the annual turkey pardon: According to the New York Times, Trump is considering granting preemptive pardons to his personal attorney, Rudolph Giuliani, as well as his oldest three children and his son-in-law before leaving office.

A U.S. president’s pardon authority is as old as the office itself, but controversy over whether and how the chief executive should exercise the privilege has persisted since the nation’s founding. Despite a rich history of pardoning controversial figures after and even before they’re convicted of federal crimes, there's still one kind of pardon of that no president has ever tested: the self-pardon. Here’s why—and whether—that could soon change.

The framers' debate on presidential pardons

At the 1787 Constitutional Convention, Alexander Hamilton proposed the president be given the power to pardon those who have committed crimes or reduce their sentences, later explaining that pardons might help “restore the tranquillity of the commonwealth” in times of rebellion. The concept wasn’t new: English laws had long given monarchs the power to grant mercy to their subjects, and the practice extended to the governors of British colonies in America.

Most of the framers agreed with Hamilton and subsequently voted down a competing last-minute proposal to deny the president the ability to grant pardons in cases of treason. Article II of the Constitution gives a president “power to grant reprieves and pardons for offenses against the United States.” The one exception enumerated in the Constitution is that presidents may not use their clemency powers to stop themselves or others from being impeached by Congress.

President have four kinds of pardon power which apply only to federal—not state—crimes. They may issue a pardon that wipes out the crime entirely, shorten or do away with a criminal sentence with a commutation, release a person from a legal obligation like a fine with a remission, or put off a person’s sentence for a period of time, known as respite.

The issue of a president’s almost unlimited pardon power was contentious enough that it factored into the decision of George Mason, a Pennsylvania delegate who feared a strong federal government, to abstain from signing the Constitution. A president with the power to pardon the treasonous, he warned, “might make dangerous use of it” by pardoning crimes in which he was a co-conspirator—which Mason believed could destroy the republic.

As it turned out, the first presidential pardons did offer mercy to men who committed treason. In 1795, President George Washington pardoned two men who had organized the 1794 Whiskey Rebellion, an uprising in western Pennsylvania in response to a costly federal tax on spirits; it took a militia of 13,000 to quell. Washington pardoned the last of the insurgents on the final day of his second term in 1797, indicating his “desire to temper the administration of justice with a reasonable extension of mercy.”

The tradition of pardoning rebels and polarizing figures continued through the years. After his election in 1800, Thomas Jefferson pardoned all of those convicted under the Sedition Act of 1798, a law passed during his predecessor's term that made it illegal to defame the government. Jefferson’s successors James Madison and James Monroe even pardoned pirates.