As President Trump comes to terms with the fact that he is entering the lame-duck phase of his presidency, he’ll probably wield the pardon pen with particular gusto. Like the presidents before him, he will review the lists of pending requests for pardons from indicted or convicted criminals that await all modern presidents at the end of their terms. The power is vast and unreviewable. No category of federal crime is off limits. Trump, whose presidency was defined by pushing the limits of executive power, can be expected to break new political and ethical ground: He has already issued high-profile pardons for former Maricopa County, Ariz., sheriff Joe Arpaio, right-wing commentator Dinesh D’Souza and Alice Marie Johnson, whose case was famously championed by Kim Kardashian.

In the coming days, Trump will probably pardon individuals in circumstances similar to those pardoned by his predecessors in the waning days of their presidencies — those lame-duck pardons have tended to fall into three broad categories. And he might try to grant the most nefarious imaginable pardon, even though it can’t be supported constitutionally: He might try to pardon himself.

Article II, Section 2, of the Constitution says that presidents “shall have Power to grant Reprieves and Pardons for Offenses against the United States, except in Cases of Impeachment.” The Supreme Court has held that this power is unreviewable, writing in United States v. Klein that the president’s pardon power “is granted without limit” and reiterating that “Congress can neither limit the effect of his pardon, nor exclude from its exercise any class of offenders.” Because pardons are a combination of mercy and largesse, they’re often issued with abandon when a president is preparing to leave office.

There are three categories into which lame-duck pardons typically fall: First, there are broad-minded, politically risky but socially important ones. On his last full day in office, President Gerald Ford pardoned, among others, World War II-era figure “Tokyo Rose.” Earlier in his term, Ford granted a conditional amnesty for Americans who had avoided the Vietnam War-era military draft, in an effort to foster national healing over one of the most divisive issues of the day. The same high-minded goal motivated Ford’s first pardon, issued a month after he took office, to his predecessor, “for all offenses against the United States which he, Richard Nixon, has committed or may have committed or taken part in” while president. Ford granted this reprieve, he said, because “conscience tells me it is my duty, not merely to proclaim domestic tranquility but to use every means that I have to insure it.”

President Jimmy Carter continued in this vein. As one of his first acts in office, he issued Proclamation 4483, a blanket pardon for Vietnam War-era draft evasion. More recently, many individuals caught up in the nation’s war on drugs have been the beneficiaries of broad-minded lame-duck pardons and commutations issued by Presidents Bill Clinton, George W. Bush and Barack Obama.

The second category of pardons is shadier. These are the 11th-hour pardons doled out to those with the right connections. Clinton’s pardon of financier Marc Rich (and his partner, Pincus Green) — while Rich lived on the lam from a raft of tax-evasion charges — is the signature pardon of this category, along with Clinton’s pardon of his former housing and urban development secretary, Henry Cisneros. These pardons may appear sleazy and are certainly inconsistent with the spirit of the power, which was described by Alexander Hamilton in the Federalist No. 74 as to ensure “exceptions in favor of unfortunate guilt” so that justice in the new republic did not become “too sanguinary and cruel.” But this kinglike, prerogative power constitutionally enables a president to be nearly as shameless as desired.

Shadier still is the third category, presidents pardoning political cronies who committed crimes related to their presidencies. Clinton’s pardon of Susan McDougal, convicted of failing to cooperate with an investigation by independent counsel Kenneth Starr, fits this mold. As does President George H.W. Bush’s pardon of six former officials involved in the Iran-contra affair. Done with the support of Attorney General William P. Barr — who serves in that role now — the pardons led independent counsel Lawrence Walsh to say “the Iran-contra cover-up, which has continued for more than six years, has now been completed.”

For Trump, the list of pardon seekers in this category is potentially long. It might include those convicted or suspected of misdeeds associated with his 2016 campaign; those who countenanced Trump’s alleged quid-pro-quo scheme in Ukraine, the subject of his impeachment trial; and those suspected of improper dealings in connection with Trump businesses.

The only person Trump can’t pardon is Trump. But that’s not what he thinks, tweeting in 2018:

The Constitution, however, and the nature of what a pardon actually is make this claim of absolute authority legally meaningless. A presidential pardon is a kind of deed. Like the deed to a house, it must be given and received; delivered and accepted. The president can no more autoimmunize himself from future prosecution than he can sell himself Trump Tower or nominate himself for the Nobel Peace Prize. Without two parties, it is both illogical and illegal. As a 1974 Justice Department Office of Legal Counsel memo put it: “Under the fundamental rule that no one may be a judge in his own case, the President cannot pardon himself.”

That does not exclude the possibility, however remote it might seem, that Trump could resign anytime between now and Inauguration Day, as part of a corrupt bargain with Vice President Pence. In that event, Pence would become the 46th president and, in exchange, could use his newly acquired presidential power to pardon Trump. Historians have looked at the possibility of a similar handshake agreement inside the Nixon administration but have never established that a deal between Nixon and Ford was made.

Such a maneuver, however, would be more than a little bit dicey for Trump. For one thing, it would run afoul of the federal bribery statute, which makes it a crime if any public official “corruptly demands, seeks, receives, accepts, or agrees to receive or accept anything of value personally or for any other person or entity” in return for “being influenced in the performance of any official act.” While an undoubtedly novel scenario that would keep lawyers and legal analysts employed for years to come, the statute is one of the few public corruption laws that clearly applies to the president.

A bigger problem, though, for Trump, would be that such a deal not only would make Trump look guilty but would be a tacit admission that he was guilty. There is a popular misconception that a pardon is an exoneration — perhaps that’s why Trump granted posthumous pardons to boxer Jack Johnson and suffragist Susan B. Anthony.

But a presidential pardon is not an exoneration. At least as far back as 1915, the Supreme Court has articulated that it carries “an imputation of guilt and acceptance of a confession of it.” In other words, if you accept a pardon, you acquiesce to your guilt to be free from the legal consequences.

But there are still consequences. Trump would have to not only forfeit his pride but also give the lie to a long record of disclaimers, most recently his assertion that he’s been described as “the most innocent, honorable man ever to hold the office of president.” For a president who has mused that his likeness should be added to Mount Rushmore, a pardon on his way out the door would bring the very penalty it is meant to erase: a story that future generations would forever know.