Updated: 4:14 p.m.

Sen. Jeff Bingaman (D-N.M.) announced his retirement on Friday, giving Republicans another open-seat pickup opportunity in 2012 — when Democrats are defending more than twice as many seats as the GOP.

The five-term Democrat, who had been favored for re-election according to recent polling, made the announcement at 3:30 p.m. in Albuquerque.

“At the end of this Congress, I will have been in public service for 34 years — four as New Mexico’s attorney general, and 30 in the United States Senate,” he said, according to prepared remarks. “The end of this Congress is the right time for me to step aside and allow someone else to serve. It is not easy to get elected to the Senate, and it is not easy to decide to leave the Senate.”

Former Rep. Heather Wilson (R) told Roll Call last month she was seriously considering running for the seat. Bingaman’s exit swings the door wide open for the former Congresswoman to run.

Wilson isn’t likely to have the field to herself if she runs. She and Rep. Steve Pearce (R-N.M.) squared off in the 2008 GOP Senate primary, which Pearce won. Pearce, who lost in 2008 and then won his old House seat back in 2010, is also on the list of potential candidates now that there is an open seat.

Potential candidates mentioned on the Democratic side include Rep. Martin Heinrich and former Gov. Bill Richardson. 

Democrats expressed confidence on Friday that they would be able to retain the seat.

“With a heavily leaning Democratic state and a potential crop of out-of-touch Republican candidates, it is clear that a we will have a strong [Democrat] who will hold onto this seat,” Democratic Senatorial Campaign Committee spokesman Eric Schultz said.

President Barack Obama won the state by 15 points in 2008, but it was far more competitive four years earlier when President George W. Bush carried it by a single point.

“Like the earlier retirements in North Dakota and Virginia, Senator Bingaman’s decision immediately presents another strong pickup opportunity for Senate Republicans,” said Brian Walsh, spokesman for the National Republican Senatorial Committee.

The Washington Post first reported Bingaman’s intentions.