Some thoughts. Alan Dershowitz has some, and so do I. His last is irrelevant to the present context; I’ve included it solely for completeness’ sake. The core of the present context is in his (3 of 3) tweet.

(1 of 3) To the extent there are inconsistencies between my current position and what I said 22 years ago, I am correct today. During the Clinton impeachment, the issue was not whether a technical crime was required, because he was charged with perjury.
(2 of 3) Therefore, I didn’t research the issue; I relied on the academic consensus that a crime was not required. In Trump impeachment, on the other hand, that is the critical issue, because abuse of power and obstruction of congress are neither crimes nor criminal-like behavior.
(3 of 3) So I have now thoroughly researched the issue and concluded that although a technical crime with all the elements may not be required, criminal-like behavior akin to treason and bribery is required.
(3 of 3 cont) To the extent therefore that my 1998 off-the-cuff interview statement suggested the opposite, I retract it. Scholars learn to adapt and even change old views as they do more research.

I disagree concerning whether criminal-like behavior is sufficient; behavior must actually be criminal to justify, legally as opposed to politically, impeachment and removal from office.

The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.

That’s a clear statement of the requirement for overt criminal behavior in order to justify the Article I, Sections 2 and 3 impeachment and trial procedure.

And yet, the President (or Vice President or any civil Officers) cannot be criminally convicted of anything. The impeachment/trial procedure under our Constitution is, explicitly, not a criminal proceeding:

Judgment in Cases of Impeachment shall not extend further than to removal from Office, and disqualification….

Guilt and acquittal simply are meaningless concepts here.

This goes further to a central point of the matter that keeps getting missed by the Republicans: Progressive-Democrats and their NLMSM keep bleating about adding witnesses, evidence, etc throughout the course of the Senate’s trial “like any other trial,” and “what kind of a trial is it without witnesses?” They keep conflating the Senate’s portion of the impeachment/trial procedure with an Article III court (or State court) trial.

In fact, the two have nothing to do with each other. The impeachment/trial procedure requires a crime in order to remove a President from office, but to convict him of that crime, he has to be haled into an Article III court for a separate, actually criminal, trial.

“Criminal-like” isn’t enough: looking, quacking, walking like a duck is insufficient here.

On the other hand, from a purely political, raw power perspective, Gerald Ford was right, and criminality becomes irrelevant: impeachable (and subsequent removal from office) is whatever Congress says it is. Which goes to the center of us being governed by less than angels. Those who have the power to make our laws also have the power to ignore their own lawlessness.

(Another central point that keeps getting missed is the Progressive-Democrats’ constant demand that the President provide his own evidence to prove his innocence. The Republican legal team and Republicans generally, keep not disputing that unAmerican contention. Kellyanne Conway finally started approaching this, tangentially, in a Monday night interview.)