John Kerry:

In his sophomore year, Kerry became the Chairman of the Liberal Party of the Yale Political Union, and a year later he served as President of the Union. Amongst his influential teachers in this period was Professor H. Bradford Westerfield, who was himself a former President of the Political Union. His involvement with the Political Union gave him an opportunity to be involved with important issues of the day, such as the civil rights movement and the New Frontier program. He also became a member of the secretive Skull and Bones Society, and traveled to Switzerland through AIESEC Yale.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Who was Kerry's most influential professor?
H. Bradford Westerfield