As President Donald Trump's days in the White House come to an end, he is expected to hand out a number of presidential pardons to political allies, family members and reportedly even himself. GBH Morning Edition host Joe Mathieu spoke with Northeastern University law professor and GBH News legal analyst Daniel Medwed about the legal limits of the president's pardoning power. The transcript below has been edited for clarity.

Joe Mathieu: Start with the basics here because it's good to go over this stuff, as we could be seeing a lot of headlines like this over the next couple of weeks. Where does the president's pardon power come from and what does it actually cover, Daniel?

Daniel Medwed: It's grounded in Article Two of the Constitution, which vests the president with the authority to, "grant Reprieves and Pardons for Offenses against the United States, except in Cases of impeachment." What that boils down to is that it encompasses both the classic pardon power — the ability to forgive people for their underlying criminal convictions — as well as the power of commutation, to commute or reduce sentences. Those two powers are not necessarily interchangeable. So, for instance, Trump has pardoned, in very high-profile instances, people like Roger Stone and Michael Flynn forgiving them for their past crimes. But with respect to disgraced former Illinois Governor Rod Blagojevich, he simply commuted his sentence — he lopped off the remaining four years of his federal prison term and stopped short of a pardon. Now, the really important takeaway about the federal presidential pardon power is that it only relates to offenses against the United States, which has been interpreted to mean federal crimes. In other words, Trump is powerless to pardon anyone, including himself, for state level criminal culpability, including potential New York state crimes.

Mathieu: And there are some investigations underway there.

Medwed: That's right.

Mathieu: As a practical matter, though, is there a procedure to this and does it include any restrictions on what the president can do?

Medwed: That's a really important question. So here's how it should work, ideally. The Department of Justice has an elaborate procedure in place for people who wish to seek clemency. You file an application with an office known as the Office of the Pardon Attorney, you wait for a long time and then there are intricate vetting systems in place to make sure that your clemency application has merit. But that's not enshrined in the Constitution. Those procedures are just norms, they're not constitutional principles, which means that the president may bypass them and basically do whatever he wants in this area, which, as is Trump's wont, he has done. He has issued a series of very personal pardons without necessarily going through the regular process. Now, to be fair, he hasn't issued an avalanche of pardons and commutations yet. As of late November, he had only made 45 clemency grants, the fewest since President William McKinley, who is president from 1897 to 1981, and far shy of the 900-plus that President Obama issued. To be fair, that number is going to soar. As you indicated at the top, there might be a blitz of pardons as he considers exercising forgiveness for political allies like Rick Gates and George Papadopoulos, who were convicted as part of the Russia investigation, as well as what are called preemptive pardons for his family members, Rudy Giuliani, and others.

Mathieu: That's the one I wanted to ask you about because I hear a lot of people talk like they know what they're talking about on this. Is there such a thing as a preemptive pardon or do you, in fact, have to list the charges you're pardoning someone from?

Medwed: That's critical. So here's how it works. Yes, in theory, you can have a preemptive pardon. They're very rare and with a lot of restrictions. So you may pardon someone for, of course, past crimes and criminal convictions; that's the classic use of the pardon. But you could also pardon them for past actions that have not yet resulted in criminal charges, much less a criminal conviction. So that's what Gerald Ford did with Richard Nixon. When Nixon stepped down, Gerald Ford issued a preemptive pardon that would cover all of Nixon's actions from 1969 until 1974 when he was in the Oval Office. But it's not a form of blanket immunity that would shield you from future actions. It's not a license for future lawlessness.

Mathieu: OK, good. We clear this up, finally! We only have 30 seconds, Daniel. Is it possible for the president to pardon himself? I know this is a big debate right now.

Medwed: It's a huge debate. It's never been done before, so we really have no idea and we don't know how the U.S. Supreme Court would handle it, if it reached the court. Though, of course, the court is pretty compliant and sympathetic to President Trump at the moment. But I will say that it flies in the face of the rationale for the pardon power, which comes from Ye Olde England. It's based on the idea that the king should be able to exact benevolence upon his subjects. And the idea of a self pardon is not grounded in benevolence, it's grounded in selfishness. So it wouldn't seem to fit. And no matter what, let's keep in mind that President Trump and anyone he chooses to pardon would still be on the hook for state law crimes.