He is also "an American lawyer and former law professor known for his work in U.S. constitutional law and American criminal law"
He also claims to be a Democrat, yet it appears he puts the Constitution above party. Thus, he defended Trump in the impeachment hearings. He has stated that the Mar Logo raid is political and a rights violation when it first happened. And he's somewhat aghast that Democrats and orgs like the ACLU aren't siding against the government in rights violation cases like this.