Democratic Sen. Tim Johnson of South Dakota will not be seeking re-election at the end of his term in 2014, NBC News confirms.
Johnson, 66, a three-term senator, will be giving up his powerful seat as chairman of the Banking Committee.
He is the fifth Democrat to announce retirement plans in recent months, shaking up prospects on whether Democrats will continue to control the Senate after the next election. Johnson's red-leaning state offers up an opportunity for Republicans who only need to net six seats in 2014 to take hold of the Senate. Mitt Romney won South Dakota over President Obama by almost 20 points in the 2012 presidential race.
Johnson's announcement was not unexpected--in 2006 he suffered a brain hemorrhage that left him partially paralyzed.
He is expected to make a formal announcement Tuesday afternoon during a conference held at his alma mater, the University of South Dakota.