Read this and answer the question. If the question is unanswerable, say "unanswerable".

Garry Trudeau, creator of the political Doonesbury comic strip, attended Yale University. There he met fellow student and later Green Party candidate for Congress Charles Pillsbury, a long-time New Haven resident for whom Trudeau's comic strip is named. During his college years, Pillsbury was known by the nickname "The Doones". A theory of international law, which argues for a sociological normative approach in regards to jurisprudence, is named the New Haven Approach, after the city. Connecticut US senator Richard Blumenthal is a Yale graduate, as is former Connecticut US Senator Joe Lieberman who also was a New Haven resident for many years, before moving back to his hometown of Stamford.

Which past U.S. senator had lived in New Haven and graduated from Yale?
Joe Lieberman