Count one more Democratic superdelegate for Barack Obama.

Sen. Jeff Bingaman will endorse the senator from Illinois this afternoon, according to a source with knowledge of Bingaman's decision.

It is not yet clear why Bingaman has decided to take sides - we'll have to wait for his statement later today. His endorsement is slightly surprising since Bingaman is typically very circumspect about signaling his intentions in Democratic primaries. Of course, this isn't just any primary election. It's one for the ages.

Gov. Bill Richardson has also endorsed Obama. Rep. Tom Udall, another top New Mexico Democrat, has yet to publicly announce who he's pulling for in this hard-fought, drawn-out Democratic battle for the nomination.

 UPDATE at 12:54 MST. Here's the official news release from Obama's campaign.

SENATOR JEFF BINGAMAN ENDORSES BARACK OBAMA

Chicago, IL – Today, United States Senator Jeff Bingaman (D-NM) endorsed Barack Obama for president, citing his ability to rise above the issues that divide us and end the war in Iraq, bring universal health care, and make America energy independent.

Senator Bingaman said, “Today, I am announcing my support for Barack Obama for president and declaring my intention to vote for him at the Democratic convention.

“Our nation faces a daunting number of critical challenges: reasserting America’s leadership in the world, meeting our needs for energy independence, addressing global warming, making healthcare accessible and affordable, positioning our economy to effectively compete globally, and extricating ourselves from the war in Iraq, to name a few. 

“To make progress, we must rise above the partisanship and the issues that divide us to find common ground. We must move the country in a dramatically new direction.

“I strongly believe Barack Obama is best positioned to lead the nation in that new direction.”

Senator Obama said, “I’m grateful today to have Senator Bingaman’s support. Senator Bingaman has been speaking out in the United States Senate on some of the most pressing issues of our time – saving our environment, fighting global warming, and making America energy independent. Senator Bingaman has been an important advocate in the energy debate, and has served the people of New Mexico for decades, giving voice to the issues that matter to families across the state.  We are proud to have his support as we fight to bring about real change for families in New Mexico and across the country.”

Senator Jeff Bingaman is the Chairman of the Senate Energy and Natural Resources Committee. He has served in the United State Senate since 1982, and previously served as New Mexico Attorney General.