Maine became the 23rd state to join the Union on March 15, 1820. Maine's first senator, John Holmes, took office on June 13, 1820, followed the next day by Maine's second senator, John Chandler. Maine's longest-serving senators include Eugene Hale (1881-1911), William Frye (1881-1911), and Margaret Chase Smith (1949-1973). The first woman to serve in both houses of Congress, Margaret Chase Smith served 24 years in the Senate, a record for female senators that remained unbroken until 2011. Among those who rose to leadership positions are William Frye, who served as the Senate's president pro tempore; Wallace White and George Mitchell, who became party floor leaders; and Margaret Chase Smith, who became the first woman to serve in a leadership position as Republican Conference chair. As vice president, Hannibal Hamlin served as the Senate's constitutional president or presiding officer.