Liberal law professor Alan Dershowitz is known for being bipartisan. He argued against the impeachment of President Bill Clinton in the 1990s and now he's doing the same on behalf of President Donald Trump, even though he voted for Trump's opponent, Hillary Clinton, in the 2016 election.

Dershowitz has repeatedly argued that his responsibility is to demonstrate that the Democrats' articles of impeachment fail to meet the constitutional requirements.

"My role is limited. I am only going to appear on behalf of the Constitution, making the arguments against impeachment based on the Constitution," Dershowitz told CNN's Michael Smerconish a couple weeks ago. "I'm not part of the strategic legal team. I won't be involved in the debate over whether there are witnesses or no witnesses or whether or not facts come out one way or another."

During the defense's arguments, Dershowitz explained the dangers of moving forward with impeaching President Donald Trump, specifically because it could be dangerous to the Constitution and the future of our country.

"Congresswoman Maxine Waters recently put it more succinctly in the context of a presidential impeachment. Here's what she said: 'Impeachment is whatever Congress says it is. There is no law,'" he recounted during the Senate trial. "But this lawless view would place Congress above the law. It would place Congress above the Constitution. For Congress to ignore the specific words of the Constitution itself and substitutes its own judgments would be for Congress to do what it's accusing the president of doing."

He's faced backlash amongst legal scholars for taking part in Trump's defense. Colleagues of his, like Jonathan Turley, have taken issue with Dershowitz's arguments because it's contradictory to what he claimed during Clinton's impeachment trial. Dershowitz says a criminal act has to take place in order for the president to be impeached, which differs from what he said in the 1990s. He said his views have changed over the last 20-something years after doing more research.

“What happened since 1998 is that I studied more, did more research, read more documents, and, like any academic, altered my views,” Dershowitz said during the trial.

The 81-year-old said the current political climate is the reason he's facing backlash.

“This is the worst controversy I have ever been in politically,” Dershowitz told The Hill. “I have some family members who won’t talk to me, I have some friends who have refused to have anything to do with me. But it shows me who my real friends are.”

Although Dershowitz has defended high-profile people, like OJ Simpson, Jeffrey Epstein and Harvey Weinstein, he said he has “mixed feelings" about taking part in Trump's impeachment trial.

“In O.J., people hated what I did. With Trump, people hate who I am,” Dershowitz told The Hill. “And there’s a big difference.”