Hawaii's new senator Brian Schatz has been sworn into office, a day after being appointed by Hawaii Governor Neil Abercrombie.
Mr Schatz, who served as Hawaii's lieutenant governor under Governor Abercrombie, took the oath of office on Capitol Hill.
The 40-year-old is a former state representative and one-time chairman of the state's Democratic Party who ran Mr Obama's 2008 campaign in Hawaii.
The selection went against the wishes of the longtime Senator Daniel Inouye, whom Senator Schatz replaces.
Mr Inouye wanted U.S. Representative Colleen Hanabusa to succeed him.