Michigan State University law professor Brian Kalt has been studying and writing about the constitutionality of a presidential self-pardon for more than 20 years.

It's a hypothetical legal question Kalt said he started looking into in law school and has been fascinated with since, even including the topic in his 2012 book "Constitutional Cliffhangers: A Legal Guide for Presidents and their Enemies."



But his work has picked up steam nationally following a Washington Post report that President Donald Trump's lawyers are looking into the president's authority to grant pardons and the limits of former FBI director Robert Mueller's investigation into Russia and any connections with the Trump campaign.

"When I wrote my book, most of the feedback I got was, 'A bunch of this stuff can never happen," Kalt said. "Most of the time no one listens -- people just mainly care about whether their side wins. But sometimes there's this window of opportunity that opens up."

So could President Trump -- or any future president -- grant a self-pardon?

Technically, no one knows, because the question hasn't been brought up in the courts and would only come up if a president went through with it and was challenged, Kalt said.

The main argument for it is that it doesn't specifically say a president can't grant a self-pardon in the Constitution. But the definition of a pardon generally implies it's being bestowed upon someone else, Kalt said, and there's also a question of whether the president could judge his own case.

"If I were a judge and this case came in front of me, I'd say a self-pardon's not valid," Kalt said.

The U.S. Constitution allows presidents to "grant Reprieves and Pardons for Offences against the United States, except in Cases of Impeachment." A presidential pardon covers only federal criminal offenses.

The most well-known presidential pardon came from former President Gerald Ford, who pardoned his predecessor Richard Nixon following his resignation over his involvement in the Watergate scandal.

Read more about Kalt's theories on this topic in his book or in a May 2017 essay he wrote for Foreign Policy.