Democratic US Sen. Tammy Baldwin announces bid for third term in battleground Wisconsin

Democratic U.S. Sen. Tammy Baldwin is seeking a third term in battleground Wisconsin. Baldwin led the charge to protect same-sex and interracial marriage in the state.

No Republicans have announced they are running for Baldwin's seat, which will be critical for Democrats to hold if they want to maintain control of the Senate.

Baldwin won her first local race at age 24 and in 1998 won a seat in the U.S. House to became the first woman whom Wisconsin voters sent to Congress. She was elected to the Senate in 2012, handing former Republican Gov. Tommy Thompson his first defeat in a statewide race, in a year when Barack Obama was also on the ballot.