The Democratic Senatorial Campaign Committee is investing precious resources to bolster Sen. Ben Nelson, even though the Nebraskan has yet to commit to running for re-election in 2012.

Since September, the Nebraska Democratic Party appears to have accessed DSCC transfers to fund about $800,000 worth of statewide television and radio ads on Nelson’s behalf, according to GOP sources who track media purchases.

Nelson said in an interview that he would decide by the end of the year whether he will seek a third term, but he disputed any suggestion that there was a connection between his decision and the DSCC’s early intervention in the race.

Nelson said family issues and how productive he can be over the course of another six years in the Senate are among his considerations. He characterized the television spots run on his behalf this fall as a “response to all the negative ads that were run about me by Americans for Prosperity and Karl Rove’s PAC, and so it’s more in that line than anything else.”

Crossroads GPS, a Republican 501(c)(4) that counts Rove as a founder, ran issue ads against Nelson during the summer-long debate over the debt limit. “You can’t just withstand a lot of negativity without having some level of response,” Nelson said, though he added that he did not communicate these feelings to the Nebraska Democratic Party or the DSCC.

“It’s a matter of leaving those decisions to my campaign manager. We discuss things, but he’s in charge of the campaign,” the Senator explained.

Nelson said whether he can win is always a factor in deciding whether to stand for office, but not a major one. Nelson campaign manager Paul Johnson said Friday that he believes Nebraska’s senior Senator will run for re-election next year, although Johnson made it clear that is only his personal opinion.

The DSCC declined to comment on its Nebraska strategy. Chairwoman Patty Murray would say only that the DSCC is “helping our candidates who are up for election. Ben Nelson is one of them.”

But knowledgeable Democratic operatives said the diminished political standing of state Attorney General Jon Bruning, who has been considered the frontrunner in the Republican primary, was one of the motivations behind the committee stepping in early to try to help soften Nelson’s path to re-election. And Democrats concede that the money spent against Nelson this year by Crossroads GPS and other conservative activist groups pushed the DSCC to act.

The Nebraska Democratic Party is not the only state affiliate to receive transfers from the DSCC. But it appears that the Nebraska party may have benefited more than others from the committee’s largess. Media tracking sources say the Nebraska party, which first went on air in late July, has bought statewide broadcast and cable television through Nov. 2 at an average of about $135,000 per week, more than enough to penetrate the Cornhusker State’s relatively inexpensive media markets.

“Republicans tried to sell a bill of goods that Nebraska is gone, and that’s not true,” one Democratic strategist said. The strategist said the DSCC’s support for Nelson has nothing to do with trying to persuade him to run for re-election: “He knows there’s going to be resources for him.”

Johnson said Nelson has not asked for any assistance from Washington, D.C., Democrats, although he is “glad” for the help.

Nelson, a centrist Democrat and former governor, was for several years a popular figure in his Republican-leaning state. But the Senator has been under fire ever since he played a crucial role in the passage of President Barack Obama’s health care law.

Republican strategists view Nelson’s seat as one of their top pickup opportunities — regardless of whether the Senator stands for re-election. And they dismiss recent optimism emanating from the DSCC as misplaced.

Of course, Nelson is not the only vulnerable Democrat going into 2012.

The DSCC is defending 23 Democratic-held seats this cycle, including many in states that either lean Republican or tend to swing with the political tide — a factor that, at this point, appears to be in the GOP’s favor.

With multiple seats conceivably threatened, Murray could be forced to make tough decisions about where to invest, although the DSCC has continued to outraise the National Republican Senatorial Committee and took in about $4 million more in the third quarter.

Sen. Jon Tester (Mont.), one of the potentially vulnerable Democrats likely to take heavy political fire from Republicans next year, has also seen ads run against him at home, including by Crossroads GPS during the summer debt ceiling debate.

Democrats who faced similar pressure during the same time period included Sens. Sherrod Brown (Ohio), Claire McCaskill (Mo.) and Bill Nelson (Fla.).

Despite having already committed to running for re-election, it is unclear whether they have received equal attention from the DSCC. Tester, at least, seemed unconcerned.

“That really is [the DSCC’s] call,” he said. “It doesn’t really matter.”

Republicans contend that the DSCC’s decision to get involved in the Nebraska race in the fall of the off-year proves the committee is worried.

“When you look at the massive spending by national Democrats in Nebraska, it certainly makes you wonder why they apparently don’t place the same premium on Claire McCaskill and Jon Tester’s re-election campaigns as they do for Ben Nelson,” NRSC spokesman Brian Walsh said.

When asked how she decides who to help “early,” Murray said that she’s “defending 23 seats and I’m working hard to make sure we defend them all.”

Sen. Bob Menendez, who served as DSCC chairman last cycle and is running for re-election this year, said Murray may have no choice but to invest early to protect certain incumbents, given the activity of third-party GOP groups.

“There are moments where you have to spend early to make sure a race doesn’t get away from you,” the New Jersey Democrat said. “Probably with the third-party expenditures taking place in his race, the DSCC probably felt that at this time they had to get engaged to make sure that race doesn’t get away from them.”