Harvard Law Professor Emeritus Alan Dershowitz, who was added to President Donald Trump's impeachment trial defense team last week, told Newsmax TV on Tuesday that he will be making a "constitutional case" later this week before the Senate against the two articles of impeachment facing President Donald Trump.

"[I will be] arguing that neither abuse of power nor obstruction of Congress are constitutionally valid criteria for impeachment," Dershowitz told Tuesday's "Greg Kelly Reports," explaining that crimes such as maladministration, corruption, dishonesty, and more were discussed by the Founding Fathers, but they only agreed on criminal criteria.

"That is, treason, that is a crime, bribery, which is a crime," Dershowitz said.

Further, when referring to the much-used phrase "high crimes and misdemeanors," one must consider if the crimes that are alleged are "akin" in severity like treason and bribery.

"Treason and bribery are serious crimes," Dershowitz said. "Not abuse of power. Half of the American presidents have been accused of power by their political opponents. The [Constitution's] framers would never have accepted abuse of power, so vague and open-ended a concept, as a criterion for impeachment."

Dershowitz also addressed the controversy concerning a video that has surfaced of him from 1998 when he said during the impeachment of then-President Bill Clinton that "it certainly doesn't have to be a crime if you have somebody who completely corrupts the office of president and who abuses trust and who poses great danger to our liberty.

"You don't need a technical crime," Dershowitz had concluded then.

"I'm correct when I said you don't need a technical crime," he told Kelly. "For example, if a president bribes somebody, but it happens outside the country or the statute of limitations is long gone, that would be enough for impeachment.

"I was wrong when I said that corruption or the other statements I used would be enough," he added.

But with Clinton, that was not the issue, as he had been charged with the crime of perjury.

"I really didn't do the research back then," Dershowitz said. "I just accepted the scholarly consensus."

But with Trump, Dershowitz said he went back and did more research and read "every single word written and spoken during the Constitutional Conventions. I read the arguments in the first of our impeachment trials against Andrew Johnson, and I became absolutely convinced that you need criminal conduct akin to treason and bribery."

He also denied his change of mind is based on a partisan view in favor of Trump, but insisted it is "just based on my review" of the law.

Dershowitz also said the evidence that Trump's actions where Ukraine is concerned, including the conversation between him and Ukraine President Volodymyr Zelenskiy, rose to a level of "any kind of crime" does not exist.

"I think you'd need a lot more information, a lot more evidence, and the House of Representatives could have tried to get it," he said. "They could have gone to court, but they didn't, so now we have a record, and the Senate will vote on whether or not that record is sufficient to conduct a trial, whether witnesses will be needed, the only thing I have to say from a constitutional point of view."

Meanwhile, if witnesses are called by Democrats then there must be a "full opportunity" for witnesses to be called by Trump's legal team, Dershowitz said.