AP sources: Sen. Ben Nelson of Nebraska to retire.

December 27, 2011 - 4:02 PM

WASHINGTON (AP) — The Associated Press has learned that Sen. Ben Nelson of Nebraska will not seek re-election next year.

Two sources say Nelson will announce his decision on Tuesday. The sources spoke on condition of anonymity because Nelson has not yet made an announcement

Nelson's retirement will make it harder for Democrats to maintain control of the Senate. Democrats will have to defend 23 seats in next year's election, compared to 10 Republican seats.

.