According to the Christian pollsters at the Barna Group, Sen. John McCain has failed to hold on to a critical part of the Republican base: born-again evangelical Christians. Even with Gov. Sarah Palin on the ticket, support from the key constituency has floundered compared to Bush’s numbers in 2004.

Meanwhile, independent groups are hitting the airwaves on Christian talk radio with ads featuring Sen. Barack Obama talking about his faith and prominent “pro-lifers” explaining — and supporting — Obama’s position on abortion.

The Barna poll found that McCain garnered the support of 63 percent of evangelical voters compared to 85 percent that Bush received in 2004. Sen. Barack Obama has slowly built his support among the socially conservative group from 9 percent in May to 23 percent in October.

Among born-again Christians in general (not including evangelicals), Obama bested McCain by a 45 percent to 43 percent margin. McCain’s 43 percent pales in comparison to Bush’s 62 percent among born-again Christians in 2004.

And Obama holds a large lead among people of faith in general: 60 percent support the Democratic candidate while less than half, 49 percent, support McCain.

Even though 10 percent of born-again Christians are undecided, even if McCain swept them, he would still fail to attract the kind of support Bush enjoyed in 2004.

And a sweep like that would be unlikely. Obama has been targeting Christian voters since the beginning of primary season, and it appears those outreach efforts are paying off. In addition, the Matthew 25 Network is hitting Christian talk radio with a series of ads explaining Obama’s faith to Christian voters, using Obama’s own statements to woo the important voting bloc.