The 25th Amendment to the U.S. Constitution is probably best known for what is in the fourth and final section, which spells out the way the president of the United States can be removed from office if they’re alive but unable to fulfill the duties of the office. But the second section—which clarifies the process for replacing a vice president—is actually worthy of consideration as well, now that President Trump has become the third president in the country’s history to be impeached, and is facing a trial in the U.S. Senate.

John D. Feerick, Dean Emeritus and the Norris professor of law at Fordham Law School, was instrumental in getting the amendment passed. In October, 1963, Feerick, then a recent graduate from Fordham Law, published an article in the Fordham Law Review on the subject, and just a month later, President John F. Kennedy was assassinated, prompting members of Congress to revisit the subject. Four years later, in February, 1967, the amendment was passed.

We sat down with him to learn more.