American University Professor Allan Lichtman was one of the few professional prognosticators to call President Trump's win in November.

Using his system of “Keys to the White House,” which postulates that presidential elections are essentially a reflection on the party in power, Lichtman said Trump was headed for the presidency. Then, just before the election, he doubled down.

And he made a second prediction, too (though, this time, without the benefit of his keys) — that Trump will be impeached before his time in office ends.

Now, he's written a whole book explaining how that could happen, titled “The Case for Impeachment,” publishing on April 18. Lichtman lays out eight ways that Trump could get in trouble, set against the historic background of previous presidential impeachments. The Fix sat down with Lichtman at his office at American University in Washington to ask him about his most recent prediction. Our conversation, below, has been edited only for clarity and length.

The Fix: You were one of the only people who called Trump’s win before November — and then you doubled down on your prediction, just before the election, adding that you predict he’ll be impeached. Take me through that process.

Lichtman: First, in September of 2016, and then on a double down in October of 2016, I predicted, against all the pundits and all the pollsters, that Donald Trump would be the next president of the United States. And I have to tell you, I took a lot of flak for that prediction. A lot of people thought I was way off base.

One of the ones who noticed, though, was Donald Trump, who wrote me a note saying, “Congratulations on your prediction.” What he probably didn’t pay attention to was, at the same time, I also predicted that although Donald Trump would be elected, he would also be impeached, becoming the first president to be impeached, of course, since Bill Clinton.

Fix: Your official prediction for the winner of the election was based on a system of keys that you tested over decades, but this latest prediction, of his impeachment, while it’s still based on history, is not based on a refined system or science. So how do you back that up? Not just your gut instinct, what’s your actual evidence?

Lichtman: Well, my prediction of a Trump victory was based on my long-standing prediction system, the Keys to the White House, which I’ve used successfully for the last nine elections since 1984. My prediction of a Trump impeachment was not based on a formal scientific system, but was based on a deep study of the history of (impeachment), the process of (impeachment) and Donald Trump’s own history. He hadn’t become president yet! But he had a long history as a businessman and someone at least peripherally involved in politics. And I put all of that deep historical study together in my new book, “The Case for Impeachment.”

This book looks at the history of impeachment — cases like that of Andrew Johnson in 1868, Richard Nixon, who resigned before he was going to be impeached, Bill Clinton. It looks at how impeachment really works, which is quite different from the way most people think it does. You don’t actually have to commit a crime to be impeached. The House of Representatives basically decides what constitutes impeachment, and it could be any violation of the public trust, whether or not it’s a crime. And finally there’s great depth in Donald Trump’s history, and at least through mid-March, the events of his presidency. And it lays out, believe it or not, eight different grounds on why Donald Trump could be removed from office.

Fix: It’s not actually that uncommon for presidents to be impeached. While it’s certainly a political disaster, it’s not necessarily a national disaster for a president to be impeached either.

Lichtman: It’s not uncommon, and America’s framers kind of believed that impeachment was a critically important element of the Constitution — to be a check on a rogue president who they believe could otherwise smash through even the checks and balances built into our system. And counting Richard Nixon, who resigned before he certainly would have been impeached, one out of every 14 American presidents has faced impeachment. You know, gamblers have gotten rich betting much longer odds than that.

And impeachments have not been national disasters. If you look back at the impeachment of Andrew Johnson in 1868, it was good for the country, not bad, because Johnson had been obstruction to Reconstruction. He had been obstructing the integration of the newly freed slave into American life, and after being chastised by impeachment, even though he wasn’t convicted by the Senate, he moderated his policies.

After the impeachment of Bill Clinton, the presidency emerged stronger than ever. It wasn’t weakened — some might even say too strong. And of course, the near-impeachment and resignation of Richard Nixon removed a clear and present danger to our democracy from office. And I believe one of the reasons Trump is vulnerable to impeachment is that he shares many of the same traits as Richard Nixon, and poses the same kind of threat to our constitutional system, our liberties and our freedoms.

Fix: But right now, Republicans control both houses of Congress and the White House. Why would House Republicans impeach their own guy?

Lichtman: Well, they’re not going to unless the American people demand it. Yes, the power of impeachment is lodged in the U.S. House of Representatives, but they are the people’s house, and they are responsive to the people.

The Republican Congress could conceivably move to impeachment if they believe Trump is a liability to them, and remember, every member has to stand for reelection in 2018. And Trump has no long-standing relationship with these members of Congress. He hasn’t really been a mainstay of the Republican Party. And there is also the possibility that in 2018 you have a wave election, which gives Democrats control of the House and completely changes the political dynamic.

But barring that, understand, not all Republicans have to be in favor of impeachment. If Democrats want it, and two dozen Republicans, approximately, switch, you have enough votes for impeachment. All it takes is a simple majority.

And finally, remember: Republicans really don’t trust Donald Trump. He’s a loose cannon. But they love Mike Pence. He’s a down-the-line Christian conservative dream president for the Republicans in Congress.

Fix: So what is it that makes you think President Trump could actually be impeached?

Lichtman: I make very clear in The Case for Impeachment that I do not believe Trump should be impeached because he’s an unconventional president, because he’s breaking the molds of tradition, or even because he’s unpopular. Rather, Trump should be impeached if and when he becomes a serious threat to our constitutional order, to our freedoms and liberties, and to the national security of the United States.

And I outline eight areas of potential removal of Donald Trump, based on his early presidency and his many decades of history as a businessman. For example, Trump has repeatedly, as a businessman, flouted the law. He kind of began his career by getting in trouble with the Department of Justice, which had a very strong case against him that he’d broken the Fair Housing Act. Reporting indicated that he’d broken the Cuban embargo in the 1990s, when that was a serious crime. Reporting also indicated that he had broken laws with respect to the employment of illegal immigrants, ironically contradicting his own campaign, and there are certainly laws that he could now break, for example, laws that ban torture.

Over the course of his entire business career, he has a pattern of playing fast and loose with the law, and letting statutes of limitations run out, settling cases, protracting lawsuits, walking away from failed deals. He also has a pattern and practice of not telling the truth. That is not just something that started when he was a candidate.

His overriding pattern is Donald Trump first, and nothing else matters nearly as much. And when you’re not president, you can get away with that, you can walk away from things. But as president, you can’t. You are accountable for what you do and for what you say. And what is the ultimate accountability for a president? That accountability is impeachment.