According to The New York Times — As President Donald Trump enters the endgame of his time in power, he is said to have consulted advisers about the possibility of granting preemptive pardons to his relatives and to allies like his personal lawyer Rudy Giuliani.

Trump has also claimed that he has “the absolute right to pardon myself,” raising the possibility that he may try to impose roadblocks against any future federal prosecution of himself. And a federal judge this week unsealed heavily redacted documents revealing that the FBI has been investigating an unidentified person for a potential pardon-for-bribe scheme.

The rising chatter about pardon issues follows closely on the heels of Trump’s pardon last week of his former national security adviser Michael Flynn and has heightened interest in the scope and limits of his clemency power. Here is what you need to know.

What is a pardon?

It is an executive power that acts as a check and balance on the federal criminal justice system, enabling a president to bestow mercy upon offenders.

The Constitution gives the president clemency powers “to grant reprieves and pardons for offenses against the United States, except in cases of impeachment.” This could be either a commutation, which reduces or eliminates a sentence imposed after a conviction for a crime, or a pardon — a broader nullification of all legal consequences for an offense.

May a president issue prospective pardons before any charges or conviction?

Yes. In Ex parte Garland, an 1866 case involving a former Confederate senator who had been pardoned by President Andrew Johnson, the Supreme Court said the pardon power “extends to every offense known to the law, and may be exercised at any time after its commission, either before legal proceedings are taken or during their pendency, or after conviction and judgment.”

It is unusual for a president to issue a prospective pardon before any charges are filed, but there are examples, perhaps most famously President Gerald Ford’s pardon in 1974 of Richard Nixon to prevent him from being prosecuted after the Watergate scandal. And in 1977, on his first day in office, President Jimmy Carter pardoned hundreds of thousands of men who had dodged the draft during the Vietnam War, enabling many who had fled to Canada to return home without fear of prosecution.

Does a pardon eliminate all risk?

No. For one thing, Trump only has clemency power over federal offenses. Some types of offenses — like tax evasion and financial fraud — are offenses under both federal and state law. Trump does not have the authority to prevent state prosecutors from pursuing charges over such a matter. State prosecutors in New York are investigating various matters related to Trump’s financial dealings.

Moreover, a pardon could increase one type of risk: By eliminating the possibility that the recipient might be federally prosecuted for a matter, it also eliminates the ability of that person to invoke the Fifth Amendment right against self-incrimination in order to avoid testifying about it. Thus, pardon recipients subpoenaed before Congress or a grand jury would be compelled to talk; if they lied or refused to testify, that would be a new crime.

May a president pardon his relatives and close allies?

Yes. The Constitution does not bar pardons that raise the appearance of self-interest or a conflict of interest, even if they may provoke a political backlash and public shaming.

Shortly before leaving office in 1993, President George Bush pardoned six Reagan administration officials over “their conduct related to the Iran-Contra affair,” including former defense secretary Caspar W. Weinberger, who was about to go to trial on charges that he had lied to Congress. The independent prosecutor, Lawrence E. Walsh, had been planning in the trial to explore whether Bush had played a greater role than he had acknowledged when he was the vice president, and Walsh accused Bush of a “cover-up.”

In 2000, shortly before leaving office, President Bill Clinton issued a slew of controversial pardons, including to his half brother, Roger Clinton, over a 1985 cocaine conviction for which he had served about a year in prison, and to Susan McDougal, a onetime Clinton business partner who had been jailed as part of the Whitewater investigation.

May a president issue a general pardon?

This is unclear. Usually, pardons are written in a way that specifically describes which crimes or sets of activities they apply to. There is little precedent laying out the degree to which a pardon can be used to instead foreclose criminal liability for anything and everything.

Notably, Ford’s “full, free and absolute pardon” of Nixon was extraordinarily broad. It covered all federal crimes Nixon “committed or may have committed” during his presidency, rather than listing particular matters or categories of activities. But because prosecutors did not try to charge Nixon, the validity of this rare, open-ended clemency was untested.

In a law journal article this year, Aaron Rappaport, a law professor at the University of California, Hastings, argued that pardons must be specific about what they are covering. He cited English common-law principles that informed the Founders’ understanding of pardons, as well as fundamental democratic values. Still, he also acknowledged that “the existence of a specificity requirement has never been acknowledged by the Supreme Court.”

May a president pardon himself?

This is unclear. There is no definitive answer because no president has ever tried to pardon himself and then faced prosecution anyway. As a result, there has never been a case which gave the Supreme Court a chance to resolve the question. In the absence of any controlling precedent, legal thinkers are divided about the matter.

Those who think a president can pardon himself point out that the relevant text in the Constitution is broadly written and contains no explicit exception precluding a self-dealing use or abuse of that power. Because the Founders did make an explicit exception for cases of impeachment, they argued, that implies they did not intend there to be any other exceptions.

But other legal thinkers have come up with theories for why the Supreme Court might nevertheless reject a purported self-pardon if it ever came up. For example, some scholars have argued that the Founders’ use of the word “grant” should be interpreted as meaning one person giving something to another, so a president cannot grant a pardon to himself.

In August 1974, four days before Nixon resigned, Mary C. Lawton, then the acting head of the Justice Department’s Office of Legal Counsel, issued a terse legal opinion stating that “it would seem” that Nixon could not pardon himself “under the fundamental rule that no one may be a judge in his own case.” But she did not explain what transformed that principle into an unwritten legal limit on the power the Constitution bestows on presidents.

Is there a way Trump might try to engineer a more clearly legal pardon for himself?

Yes. He could get Vice President Mike Pence to do it for him, using the 25th Amendment.

This part of the Constitution provides a mechanism for temporarily making the vice president the “acting president” when a president is disabled from carrying out his duties. In 2002 and 2007, for example, when President George W. Bush was preparing to be sedated for colonoscopies, he briefly handed the powers of the presidency to Vice President Dick Cheney.

In her 1974 memo, Lawton argued that it would be lawful for a president to declare himself temporarily disabled, receive a pardon from the vice president and then resume his role as president.

Would a corruption-tainted pardon count?

Probably. The Constitution does not create any explicit exception that invalidates pardons that were granted under dubious circumstances — like if a president took money in exchange, or was buying the silence of a witness to his own wrongdoing. Grants of clemency are widely understood to be irrevocable.

Still, a president who grants a pardon under corrupt circumstances could open himself up to prosecution for acts like bribery or obstruction of justice after he leaves office. Even Attorney General William Barr, who embraces a maximalist ideology of executive power, testified during his confirmation hearing that if a president pardoned someone in exchange for a promise not to incriminate him, “that would be a crime.”