Wisconsin's Tammy Baldwin is among a dozen new U.S. senators taking the oath of office.
Vice President Joe Biden swore in the 12 new senators Thursday, as well as those who won another term.
Democrats tightened their grip on the Senate with 55-45 edge following the November elections.
Baldwin is Wisconsin's first female senator and also the first openly gay candidate ever elected to the chamber. She defeated former Gov. Tommy Thompson, who had never before lost a statewide race.