Biden forgets he was vice -President.
He did officially become a professor after he was vice-President, not Senator.
“In 2017, Biden was named the Benjamin Franklin Presidential Practice professor at the University of Pennsylvania, where he intended to focus on foreign policy, diplomacy, and national security while leading the Penn Biden Center for Diplomacy and Global Engagement.[5]”
I don’t think it was anymore than a ceremonial position, meant for fund-raising.