"After 40 years, I just feel it's somebody else's turn, " Mr. Harkin said in a statement.

WSJ: Harkin's Exit Heralds Scramble for Senate Seat

Harkin said that right was given to workers in 1935, but they've since lost that right to management.

NPR: Card-Check Legislation Introduced In House

Democrats "may have to do what Mr. Lieberman wants, " Harkin said.

CNN: STORY HIGHLIGHTS

Harkin press secretary Allison Dobson said Dean's ability to attract new members into the party was a major factor in Harkin's decision.

CNN: Iowa Sen. Harkin endorses Dean

Republicans said that Mr. Harkin's retirement would put Democrats at a disadvantage.

WSJ: Harkin's Exit Heralds Scramble for Senate Seat

Tom Harkin, D-Iowa, said Monday morning.

CNN: STORY HIGHLIGHTS

Tom Harkin, the Democratic committee chairman, said in his prepared opening remarks at the hearing.

NPR: Labor Nominee Perez Pledges Open Mind

Harkin joins Senator Jeff Merkley and Colorado Congressman Jared Polis who also said they welcome this -- from the President.

WHITEHOUSE: Press Briefing