(CNN) On Friday morning, President Donald Trump fired off this tweet about fired FBI Director James Comey: "Is everybody believing what is going on. James Comey can't define what a leak is. He illegally leaked CLASSIFIED INFORMATION but doesn't understand what he did or how serious it is. He lied all over the place to cover it up. He's either very sick or very dumb. Remember sailor!"

It's the latest in a series of attempts by Trump to tar Comey with the "leaker" label. Comey has pushed backed, insisting that what he did -- giving unclassified memos to a friend to disseminate to the media in hops of forcing the appointment of a special counsel -- was not only entirely lawful but also in the public's best interests.

So, is Comey a leaker? A liar? Or a concerned citizen? In search of answers, I reached out to Heidi Kitrosser , a law professor at the University of Minnesota Law School, who specializes in " the constitutional law of federal government secrecy and on separation of powers and free speech law more broadly ." Our conversation, conducted via email and lightly edited for flow, is below.

Cillizza: Let's start simple: Define "leak" in the context of the federal government.

Kitrosser: At the most basic level, a "leak" in this context means the unauthorized disclosure of information. That might range from a disclosure that is merely indiscreet -- say, of information that one's boss would prefer not be shared because it's embarrassing -- to a disclosure that conveys classified information to a person not cleared to receive it. In the context of the great Trump-Comey War of 2017-2018, Trump is alleging that Comey engaged in the latter type of leak -- that is, that Comey leaked classified information to the media, the public, or to others not cleared to receive it.

Cillizza: What makes a leak a potential criminal act?

Kitrosser: Focusing on the classified information context, there are a few potentially relevant statutes.

The broadest and most important one is the Espionage Act. Among other things, the act criminalizes the willful dissemination, "to any person not entitled to receive it," of any documents "relating to the national defense," or any "information relating to the national defense which information the possessor has reason to believe could be used to the injury of the United States or to the advantage of any foreign nation."

You might notice that the quoted language does not specifically reference classified information. Indeed, the Espionage Act in its original form was written in 1917, long before the US government had a classification system in place. However, courts have read the "not entitled to receive it" language in light of the classification system. In other words, they interpret the language to mean that only those persons who are authorized, under the classification system -- which is largely a product of executive order and related regulatory actions -- to receive classified information are entitled to receive it under the terms of the Act. Given the breadth and malleability of the act's remaining requirements, the bare fact that information is classified often will be enough to bring it within the act's scope.

Cillizza: Explain the difference between whistleblowers and leakers.

Kitrosser: I think that there are at least two senses in which one can answer that question.

The first is in a colloquial sense focused on ethics and morality. Colloquially, I think that most people think of "whistleblowers" as persons who justifiably reveal wrongdoing. So from that perspective, a "whistleblower" is someone who is morally or ethically correct -- perhaps even duty-bound -- to reveal information, despite the fact that their superiors might not want them to do so.

Leaking, on the other hand, is a more morally and ethically ambiguous term. At best, it's morally and ethically neutral, and at worst it's used as a pejorative.

Importantly, however, those particular laws do not cover the disclosure of classified information. Persons who convey classified information without authorization receive far less protection. Most notably, they are subject to prosecution under the Espionage Act. Indeed, Edward Snowden has said that he believes he could not get a fair trial were he to return to the US, because under the Espionage Act, it makes no difference if your disclosure revealed wrongdoing or served the public interest.

Cillizza: Donald Trump has repeatedly accused James Comey of illegally leaking the classified contents of memos he wrote. Comey has said he leaked unclassified information. How big a distinction is that?

Kitrosser: It's a very big distinction. Most importantly because a leak of classified information might implicate the Espionage Act, whereas a leak of unclassified information is unlikely to do so.

The distinction also has political resonance. Among other things, Trump clearly is trying to gain the political high ground by suggesting that Comey leaked classified information and somehow put America's national security at risk. Comey, in turn, maintains that the information was not classified and that the disclosures served the public interest.

Cillizza: Finish this sentence: "Donald Trump's accusations regarding leaks are _________." Now, explain.

Kitrosser: "Donald Trump's accusations regarding leaks are self-serving."

If this were a spoken conversation, this would be the part in which I sputter helplessly while trying to decide where to begin! But I suppose I'll put it this way: Trump is a guy who couldn't get enough of WikiLeaks throughout the 2016 campaign, and who, to put it mildly, has not exactly demonstrated concern or facility for keeping a lock on the vast trove of national security information to which he has access as President. So I find it, um, interesting, to witness his professions of concern that Comey's written recollections revealed information that may or may not have retroactively been deemed classified.

I should also mention, for context, that the classification system is notoriously overbroad. It thus is entirely possible that, of the thousands of persons with original classification authority, one might retroactively classify a memo that its author and informed others consider entirely innocuous from a national security perspective.