Patrick Joseph Leahy (; born March 31, 1940) is an American politician and the senior United States Senator from Vermont. He has been in office since 1975. A member of the Democratic Party, Leahy served as the President pro tempore of the United States Senate from December 17, 2012 to January 6, 2015. As President pro tempore, he was third in the presidential line of succession. He is the most senior senator and took office at a younger age than any other current senator. Leahy received the title of President pro tempore emeritus upon the commencement of the 114th Congress. He is the last remaining member of the Senate to have served prior to the 1976 election of President Jimmy Carter.