Harvard constitutional law professor Laurence Tribe urged the GOP-controlled Senate to allow witnesses to testify in the impeachment trial of President Donald Trump ― or risk setting a “terrible” precedent for the country.

On Tuesday’s broadcast of MSNBC’s “The Last Word with Lawrence O’Donnell,” Tribe argued the only way to hold a fair trial was for lawmakers to vote to hear from Trump’s former national security adviser John Bolton “and other witnesses and the evidence.”

Bolton reportedly confirms the Democrats’ case for impeachment in his forthcoming book “The Room Where It Happened,” in which he writes Trump tied military aid for Ukraine to its announcement of a probe into Joe Biden.

Tribe described the defense argument being made by Trump impeachment lawyer Alan Dershowitz as “remarkably absurd and extreme and dangerous.”

“Namely, it doesn’t matter if a president uses the vast powers of his office to shake down an ally and help an adversary in order to get dirt on an enemy and corrupt an election,” he said, summarizing Dershowitz’s argument.

Tribe also said senators risked “leaving a message to future generations, to future presidents, that any way they want to abuse the power of their office is just fine because Trump got away with it since the ultimate ruling was, ‘so what? It doesn’t matter.’”

“You will harm not only the country today, but you will leave a lesson for future presidents that will be terrible to the Republic,” he warned GOP senators. “It will not be a constitutional democracy but it will be a dictatorship.

Concluded Tribe:

So I implore you, if you are inclined to vote to acquit this president, don’t do it on the ridiculous basis that abuse of power, because it’s not a statutory crime and is rather open-ended, is not a basis to remove. Don’t do it on that basis. Do it perhaps on the basis that after you’ve heard John Bolton and looked at the evidence, you’re just not convinced.

Check out the clip above.