BY CHRISTINA HARTMAN

Retirements are usually cause for celebration. But when it’s a member of Congress -- often -- the only one celebrating on Capitol Hill is the other party.

SEN. BEN NELSON (D-NE): “Simply put, it is time to move on. I encourage those who will follow in my footsteps to look for common ground and to work together in bipartisan ways to do what is best for the country, not just one political party.”

Senator Ben Nelson was the only Democrat in Nebraska’s congressional delegation. But perhaps more importantly -- he’s one of seven Democrats set to retire this cycle -- leading Fox News to ask:

“Does Ben Nelson's decision create another opportunity for Republicans to take back the Senate in 2012?”

Republicans sure hope so. And Politico’s David Catanese says, it’s possible: Democrats’ majority in the Senate is pretty slim. And...

“In addition to Nebraska, the party must fend off robust Republican challenges in open-seat races in North Dakota, Virginia, Wisconsin, Hawaii, New Mexico and Connecticut.”

But Nelson was a moderate Democrat, who often crossed the aisle to vote with Republicans.

The Hill notes, Democrats don’t seem to have many competitive options in the race to replace him.

Though the publication says -- some are pointing to former Senator Bob Kerrey as the party’s last best hope.

We should note Kerrey recently told a Nebraska publication it was quote “highly unlikely” he would run. Still Bloomberg’s Al Hunt looks at the odds.

“Well, it’s a little blow Scarlett in the sense that Nelson was probably about an even bet. If Bob Kerrey runs, he would be a stronger candidate than Ben Nelson. He probably will not. Meaning the democrats have an impossible task. So they’ve gone in Nebraska from an even bet to a probable loss.”

But The Washington Post’s Chris Cillizza says this isn’t that much of a loss for Democrats -- writing the seat was gonna be tough to hold onto either way.

“In truth, many Republicans already taken to counting Nebraska in their ‘win’ column along with the open seat in North Dakota. … While Nelson bowing out strengthens Republicans’ chances in Nebraska then, it doesn’t fundamentally alter the underlying math for GOPers to win back control of the Senate.”