Legal scholar Alan Dershowitz writes in a new book that the Supreme Court could intervene if President Trump is impeached, overturning a congressional vote to remove him from office for “collusion” with Russia during the 2016 election.

Even if public evidence of collusion were to emerge, the Harvard Law School professor emeritus writes in "The Case Against Impeaching Trump" that it would not be a crime, contending Trump could collude to let Russia retake Alaska without grounds for removal from office.

"It's not a crime to collude with a foreign government. Maybe it should be, but it's not," he told the Washington Examiner ahead of the book's Tuesday release.

Dershowitz argues in the book that collusion would be a "political sin" that doesn't meet the Constitution’s specification of “treason, bribery, or other high crimes and misdemeanors" for removal from office.

Judicial review might be triggered, he writes, because “this president (and perhaps others) might well refuse to leave office if Congress voted to impeach and remove him based on ‘offenses’ that were not among those enumerated in the Constitution."

"A Supreme Court that inserted itself into the Bush v. Gore election in order to avoid a constitutional crisis might well decide to review a House decision to impeach and a Senate decision to remove a president who is not accused and convicted of a specified constitutional crime," Dershowitz adds.

The chief justice of the Supreme Court, who presides over Senate trials if a majority of the House votes to impeach, arguably would be able to rule on a motion to dismiss legally invalid charges, Dershowitz writes.

"The decision by the framers to have the chief justice preside over the trial of a president may suggest that the decision was not intended to be entirely political. Indeed, it would be wrong for the chief justice to participate, much less preside over, an entirely political process. Judges are required to stay out of politics," he writes.

Although a Democrat, Dershowitz has spent much of the past year arguing on TV that Trump has been treated unfairly in the ongoing special counsel investigation of possible campaign collusion with Russia. His new book is largely a rehash of his recent commentary, containing 34 re-published op-eds and transcripts from his TV appearances.

A 28-page introduction expands on his legal arguments against impeaching Trump based on publicly unknown facts, using more extreme hypotheticals, such as allowing Russia to retake Alaska, to demonstrate what he sees as the Constitution’s requirement of criminality.

“Assume [Russian President Vladimir] Putin decides to ‘retake’ Alaska, the way he ‘retook’ Crimea. Assume further that a president allows him to do it, because he believed that Russia has a legitimate claim to ‘its’ original territory,” Dershowitz writes. “That would be terrible, but would it be impeachable? Not under the text of the Constitution.” He writes that impeachment would be possible, however, “if he did it because he was paid or extorted.”

Dershowitz told the Washington Examiner he wrote the book as an authoritative case against impeachment ahead of a potential Democratic takeover in Congress. At points in the book, he counters arguments from fellow Harvard scholar Laurence Tribe, who also wrote a recent book on impeachment, To End a Presidency.

Dershowitz said he was motivated to write the book by people such as “that jerk” Richard Painter, an ex-Republican law professor running for Minnesota Senate as a Democrat on a pro-impeachment platform, and “extremist” Rep. Maxine Waters, D-Calif. Dershowitz said he will ask his publisher to send Waters a copy.

Waters argued last year that "impeachment is whatever Congress says it is. There is no law.”

Dershowitz notes in the book that similar "extreme" remarks were made by former President Gerald Ford in 1970, when he was a member of the House of Representatives. Ford argued: “An impeachable offense is whatever a majority of the House of Representatives considers it to be at a given moment in history; conviction results from whatever offense or offenses two-thirds of the other body considers to be sufficiently serious to require removal.”

Still, without evidence that Trump committed a specific crime — in the case of treason, defined in a manner Dershowitz believes would be inapplicable — there may be avenues to overturn a congressional ruling through the judiciary, Dershowitz said.

Dershowitz cites in his book two former Supreme Court justices — Byron White and David Souter — as suggesting there may be room for court oversight of impeachment decisions.

Although his defense of Trump has made him a pervasive TV guest, Dershowitz told the Examiner “it’s been the opposite of lucrative, completely,” with speaking engagements canceled and other invitations withheld. He said he won’t make much money off the new book — which goes for $13.19 for a Kindle version, or $19.79 for a hardback copy.

"I'm acting purely in a responsible capacity because the ACLU is dead in the water," he said. "The ACLU has made a fortune of money going after Trump and they would not endanger their financial base by saying anything to defend Trump's civil liberties."

The president and legal director of the ACLU previously told the Washington Examiner that they reject Dershowitz's claim of bias.

Dershowitz's new book concludes claiming motivation from history, particularly the anti-communist red scare of the 1950s. He quotes some unpleasant email messages from critics, including a message addressing him as “Alan ‘Goebbels’ Dershowitz” and predicting that he will “be remembered as a liar and a phony.”

Although one of his top defenders, even Trump has given mixed reviews. Dershowitz said one of his most recent calls from Trump was "to correct something I said on television." He declined to elaborate.