Updated at 12:15 p.m. ET.
Sen. Barbara Mikulski, D-Md., who has served in the Senate and in Congress longer than any other woman, says she will not seek a sixth term in 2016.
Mikulski, 78, announced her decision Monday in Baltimore.
" 'Do I spend my time raising money, or do I spend my time raising hell?' " she said she asked herself, according to The Associated Press.