To the Editor:

Re “Why Did Alan Dershowitz Say Yes to Trump?” (Op-Ed, nytimes.com, Jan. 22):

Stephen Harper asks why I said “yes to Trump.” I think he knows the answer, having been in my class at Harvard Law School. Throughout my career I have stood on principle, representing people with whom I disagree as well those with whom I agree. I have never made a distinction based on partisanship.

During the Richard Nixon impeachment, as a national board member of the American Civil Liberties Union, I urged that organization to monitor the proceedings in order to protect Mr. Nixon’s civil liberties, even though I personally supported his impeachment. During the proceedings against President Bill Clinton, I testified in his favor and consulted with his defense team.

While it is true that most other constitutional scholars believe that impeachment can be based on completely noncriminal type behavior, such as abuse of power, my independent research conducted over the past two years has led me to the opposite conclusion — a conclusion shared by Justice Benjamin Curtis, who after resigning from the Supreme Court in protest of its decision in the Dred Scott case represented President Andrew Johnson, with whose politics he thoroughly disagreed.

Mr. Harper’s claim that I am not an expert in constitutional law is belied by the fact that I taught constitutional criminal procedure at Harvard Law School for nearly half a century. Were I arguing on behalf of impeachment, my credentials would not be questioned by those who question them now for partisan reasons.