David Gergen has been a White House adviser to four presidents and is a senior political analyst at CNN. A graduate of Harvard Law School, he is a professor of public service and the former director of the Center for Public Leadership at the Harvard Kennedy School. The opinions expressed in this commentary are his own. View more opinion on CNN.

(CNN) As the House voted to impeach President Donald Trump on Wednesday, he addressed a rally in Michigan and said, "By the way, it doesn't really feel like we're being impeached." In that moment, the difference between Trump and former Presidents Richard Nixon and Bill Clinton became starkly clear.

David Gergen

It's clear that Nixon and Clinton behaved very differently from Trump when faced with impeachment proceedings that clouded their presidencies. During their respective impeachment inquiries, both Nixon and Clinton ultimately cooperated with authorities. While Nixon resisted turning over information, he did yield to public pressure and let key witnesses testify. And he eventually turned over the infamous Watergate tapes when ordered by the Supreme Court. Clinton, on the other hand, agreed to testify after establishing predetermined conditions

More to the point, both Clinton and Nixon were contrite and accepted responsibility for their behavior. Nixon, for one, resigned and said , "I regret deeply any injuries that may have been done in the course of the events that led to this decision. I would say only that if some of my judgments were wrong, and some were wrong, they were made in what I believed at the time to be the best interest of the nation." After Clinton was acquitted, he issued a public apology and went back to work, putting his grudges behind him.

Thus, the case was successfully closed, the controversy resolved. More importantly, the country's checks and balances held, and the oversight responsibility of Congress was honored.

Consider how different this impeachment process has been. Trump has been belligerent and defiant throughout. He has not turned over a single document to Congress and the White House has blocked key witnesses from testifying. His supporters have argued that the evidence supporting Trump's impeachment is thin, never acknowledging it might well be bolstered if the President cooperated.

Read More