Nebraska Sen. Ben Nelson’s (D) decision to leave the Senate in 2012 clearly makes it more difficult for his party to hold his seat but may not have that large an impact on the national Senate playing field.

View Photo Gallery: Sen. Ben Nelson, the Democrat from Nebraska, will not seek reelection in 2012.

Here’s why.

Nebraska was always going to be a very tough race for Democrats. While Nelson won races in 2000 and 2006, the state’s clear Republican lean — President Obama won just 42 percent in the state in 2008 — made the race a decided longshot even with a proven commodity like Nelson in the race.

“He’ll be missed as a vote for [Harry] Reid for leader, but he had a very, very hard race against tough odds,” said Jim Jordan, a former executive director at the Democratic Senatorial Campaign Committee and now a party consultant.

(With Nelson gone, the race verges on unwinnable for Democrats — although party strategists insist that former Sen. Bob Kerrey, who has spent the better part of the last decade as president of the New School in New York City, is genuinely interested in running. Reached Tuesday in India, Kerrey didn’t address his own interest but said that Nelson’s retirement was “a big loss for Nebraska”.)

In truth, many Republicans already taken to counting Nebraska in their “win” column along with the open seat in North Dakota. (Democrats dispute the idea that the North Dakota open seat won’t be competitive but, like Nebraska, the state’s decided GOP tilt makes it tough sledding.)

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.

Give Republicans Nebraska and North Dakota and they are one seat short of the majority if the GOP nominee ousts President Obama next November. Republicans need to net two seats short if Obama is re-elected to a second term.

The majority still will come down to a handful of seats — Missouri, Montana, Virginia, Florida, Ohio — that both parties acknowledge are likely to be very, very close. Democrats now have marginally less margin for error but, in truth, they never had much room to slip if they want to stay in control of the Senate in 2013.

“It’s a big loss but control of the Senate is not as controlled by the map as many think,” said Steve Murphy, a veteran Democratic consultant, of the Nelson retirement “If Obama is re-elected, and I think he will be, Democrats will hold the Senate.”

That doesn’t mean, however, that Nelson’s retirement doesn’t have any impact on the national landscape.

The biggest ripple effect it will have is financially where national Republicans would have had to spend heavily to pry Nelson out of the seat. While a Kerrey candidacy might make the race competitive, if he decides not to run it’s very likely that both parties will simply write the race off — ala North Dakota in 2010. (Of course, you could also make the counter argument that Nelson’s retirement will allow Senate Democrats to stop throwing good money after bad.)

Outside of Nebraska, the Nelson retirement should help Senate Republicans raise money — particularly in the near-term as it will drive chatter about their prospects of taking control of the majority. Momentum matters when it comes to raising money and Republicans will — and should — paint the Nelson retirement as a sign that they are now fully on offense.

To be clear: The Nelson retirement isn’t good news for Senate Democrats. But it is far from a death blow to their hopes of retaining the majority either.

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