Not a lot of things have gone the Democrats' way this year, but dozens of their House candidates are getting a late boost from an unusual source: the National Rifle Association.

So far this year, the NRA has endorsed 58 incumbent House Democrats, including more than a dozen in seats that both parties view as critical to winning a majority.

The endorsements aren't the result of a sudden love for a party with which the NRA is often at odds. Rather, the powerful group adheres to what it calls "an incumbent-friendly" policy, which holds that if two candidates are equally supportive of gun rights, the incumbent gets the nod.

The policy has been in place for some time, and the NRA has always backed a number of Democrats, but the group's choices have become especially contentious this year because control of Congress is at stake and because so many gun-supporting Democrats were elected over the past four years.

The policy is frustrating Republicans who think the group is hurting its own cause and the party's chances next month.

In South Dakota, Rep. Stephanie Herseth Sandlin (D) got the NRA's endorsement even though her opponent, Kristi Noem (R), has made her fondness for hunting a prominent part of her campaign.

Noem's campaign manager, Joshua Shields, said that regardless of Herseth Sandlin's record on gun issues, she would still support House Speaker Nancy Pelosi (D-Calif.), "one of the most anti-gun speakers Congress has ever had."

"We made that argument to the NRA," Shields said. "Obviously it didn't work."

The thumbs-up from the NRA has given Democrats who represent conservative districts, such as Herseth Sandlin, an opportunity to fight back against repeated attacks that they're tied to their party's liberal leaders in Washington. With an NRA endorsement in hand, candidates are able to assert that they are willing to choose their constituents over their leaders when warranted.

Conversely, the NRA is so closely associated with the Republican Party that GOP candidates with impeccable records on gun rights are left to explain why they didn't get the group's backing.

At a gathering of volunteers for Robert Hurt's (R) campaign in Charlottesville last week, a concerned supporter asked the candidate why the NRA nod went to his opponent, freshman Rep. Tom Perriello (D-Va.).

Hurt said he was unhappy with the group's decision and attempted to explain the NRA policy, before also trying to link his opponent to Pelosi. "There is no more anti-Second Amendment vote than a vote for Nancy Pelosi for speaker," Hurt said.