Political forecaster Allan Lichtman got a surprise in the mail from the desk of Donald Trump shortly after the U.S. election — a personal note, handwritten directly on a Washington Post article about his work.

The story detailed how the American University history professor broke from the pundits and pollsters to conclude that Trump would take the presidency.

"Professor — congrats — good call," Trump had written in black marker, weeks before he was to be sworn into the Oval Office.

"I thought it was a wonderful gesture," said Lichtman, who has been dubbed the "prediction prof" by Politico.

A scan of the handwritten note that Lichtman received from Donald Trump shortly after the 2016 election. The note reads: 'Professor — congrats — good call.' (Courtesy Allan Lichtman)

If the president was happy with Lichtman's analysis then, he might not be so thrilled with this next prediction: "the prediction of impeachment," as Lichtman calls it. He expects the House of Representatives will formally vote that the Senate should try, convict, and remove the President from office within his first term.

8 'grounds for impeachment'

Unlike his 13 "keys to the White House" algorithm for picking future presidents, Lichtman's new book, The Case For Impeachment, lays out eight "grounds for impeachment" that are not based on a mathematical system but what Lichtman describes as a "deep study of the history" of impeachments and Trump's own history.

His new deduction has made a splash by virtue of who Lichtman is. When political statisticians came to a near-universal conclusion in the lead-up to last year's election that Clinton would handily defeat Trump, Lichtman was a conspicuous holdout.

"It was flying in the face of every pundit and pollster and statistician in America," he said. "I got a huge amount of flack for my prediction. I kept telling people: 'That's not an endorsement.'"

U.S. President Donald Trump could be the third president in U.S. history to be impeached, according to the political forecaster who also projected accurately that Trump would win the 2016 election. The only two presidents to be impeached were Andrew Johnson and Bill Clinton, though both were acquitted by the Senate. (Carlos Barria/Reuters)

To some, Lichtman's argument for impeachment proceedings is made all the more compelling by his track record. He considers his streak of predicting popular-vote winners to be unbroken since 1984. He predicted Al Gore would win the 2000 election — a call that he hung on the importance of the popular vote, which he acknowledges is no longer important in razor-thin elections. "To say I was flatly wrong in 2000 is ridiculous," he said.

Hillary Clinton ended up winning the popular vote by 3 million people in 2016. "[The keys system] is 35 years old and things change," Lichtman said. "And I've said this many times, that the popular vote in a close election doesn't matter anymore."

'Not that simple'

Predicting an impeachment, though? That's a different beast than forecasting an election, say constitutional experts.

"It's just not that simple," says Susan Low Bloch, one of the 19 constitutional scholars who testified before the 1998 House judiciary committee on the impeachment of president Bill Clinton. The impeachment process was "supposed to be really hard" by design, she says, because the very act of impeachment seems so undemocratic.

"You are undoing a national election, and I can't think of anything more serious politically than undoing an election," Bloch said. "Whether you like Trump or not, he's now the president until he's done something impeachable — which he hasn't, so far as we know."

A portrait of Andrew Johnson, U.S. president from 1865 to 1869. Johnson became the first president to be impeached in 1868, for violating the Tenure of Office Act by removing Secretary of War Edwin Stanton from the cabinet. (Library of Congress)

The history of impeachments runs shallow. Only two out of the previous 44 presidents have been subjected to the constitutional remedy for a president's wrongdoing: Andrew Johnson in 1868 and Clinton in 1998. Both were acquitted by the Senate and remained in office.

Impeachment is not synonymous with removal from office, which only occurs once the impeached party is convicted in the Senate by a two-thirds "supermajority" vote. Republicans currently have control of 52 of the seats in the 100-seat chamber.

Lichtman, slicing the data another way, argues impeachment is "not as rare as we think." Counting Richard Nixon, who would likely have been impeached over Watergate had he not resigned in 1974, Lichtman says "one out of 14 presidents have been impeached."

An 'earthshaking' scandal

Still, to initiate impeachment proceedings in the House would require overwhelming public support for legislators to consider forming the judiciary committee.

The committee would have to find the person has committed specific articles of impeachment — treason, bribery or "high crimes or misdemeanours," a catchall term vague enough to permit impeachment "even in the least appropriate cases," says Harvard University Constitutional law professor Laurence Tribe, like "the garden-variety offence" of lying under oath about a prior sexual affair.

Perhaps the most innovative of my grounds is the 'crime against humanity,' which we typically associate with genocide. - Allan Lichtman

Republicans used the "high crimes" reasoning in 1998 to impeach a Democrat on perjury and obstruction of justice after Clinton lied about his affair with Monica Lewinsky. But Trump belongs to the same party that controls Congress.

"It would be tricky for Trump to be impeached in a Republican-majority House," Tribe says, noting that Lichtman's prediction assumes that either the Democrats will win control of the House in the November 2018 mid-term elections and are convinced Trump needs to go, "or that there will be a scandal ... so earthshaking that even Republicans including Speaker Ryan will turn on their own before the mid-term elections."

Presumably such a scandal would involve "treasonous collaboration with Russia to steal the presidency," he says.

Bill Clinton was impeached on perjury and obstruction of justice in 1998 in a House vote, though he was able to stay in office because a Senate trial never convicted him. (Win McNamee/Associated Press)

Lichtman's impeachment argument comes down to eight concerns, from Trump's flouting of laws such as the Fair Housing Act in the 1960s, to business conflicts of interest that might run afoul of the emoluments clause, to what he calls "the Russia connection," which he believes could be a potentially treasonous offence.

"Perhaps the most innovative of my grounds is the 'crime against humanity,' which we typically associate with genocide," Lichtman says, hanging his argument on the International Criminal Court's prioritization of crimes against the environment as acts that could threaten human well-being and survival.

What Licthman is still missing to strengthen his case for impeachment is hard proof of wrongdoing, Bloch argues. Speculation and conjecture about Trump's Russia connections won't cut it in a Senate trial.

"I don't know what [the Senate and House intelligence committees] are going to find out about Russia, but so far there's nothing," she says. "If Trump would ever reveal his taxes, we would find out more, and if we find out more about the election and the Russian hacking, there's something maybe there, but I don't think there's anything there right now."

Lichtman knows impeachment wouldn't be easy. He nevertheless expects things to go the way he predicts for a president he sees as eminently impeachable.

"I just don't think he has the temperament, the history or the qualifications to be president," he says. "I hope he proves me wrong."