Democratic U.S. Sen. Tim Johnson of South Dakota announced Tuesday that he would retire at the end of his term, acknowledging he remains limited by a recent "health crisis" and wants to spend more time with his grandchildren.

Democratic Sen. Carl Levin of Michigan says he will not seek re-election next year.

Rep. Steve King (R-Iowa) is hitting back against American Crossroads President Steven Law in a new fundraising e-mail, declaring: "Nobody can bully me out of running for Senate."

King, a deeply conservative congressman with a tendency to make controversial utterances, has come under scrutiny from Republican strategists who worry he will make a bid for retiring Democratic Sen. Tom Harkin's seat.

Iowa Rep. Bruce Braley says he will run for the U.S. Senate seat being vacated by Democratic Sen. Tom Harkin.

Senate Majority Leader Harry Reid said Sunday he is confident that fellow Democratic Sen. Robert Menendez “did nothing wrong” by associating with a major political donor who is purportedly under FBI investigation, but he will wait for outcome of Senate ethics probe.

Brian Schatz symbolized a generational change in Hawaii's Senate delegation, taking the hand of his new colleague, 88-year-old Sen. Daniel Akaka, moments before being sworn in Thursday as the successor to the late Democratic Sen. Daniel Inouye.

President Barack Obama says the late Democratic Sen. Daniel Inouye showed him "what might be possible in my own life."

Democratic Sen. Ben Cardin of Maryland wants to scrap an amendment Sen. John McCain (R-Ariz.) added to the Senate's 2013 National Defense Authorization bill that would require a specific level of cuts for the Defense Department's civilian and contract workforce.

Democratic Sen. Ben Cardin of Maryland wants to scrap an amendment Sen. John McCain (R-Ariz.) added to the Senate’s 2013 National Defense Authorization bill that would require a specific level of cuts for the Defense Department’s civilian and contract workforce.

Former SD Gov. Mike Rounds officially announced his candidacy for US Senate in a news release Thursday morning.

— David Montgomery (@ArgusMontgomery) November 29, 2012

The former Republican governor's decision to run for Democratic Sen. Tim Johnson's seat was not seriously in doubt -- he's already formed an exploratory committee, he's planning three stops around the state Thursday, and close friends told reporters he was in the race.