Sorry to be the wet blanket here, but I have one big question. Was there any difference in the definition of Catholic between the 2008 poll and the current one? Unlike most denominations, people tend to stay “Catholic” even if they haven’t gone to church for years. I could easily see 50% of the total number supporting Obama but only 25% of the ones who go to mass weekly doing so. Unless the same criteria were used this poll might not be showing any real shift.
Catholic is the only denomination identified for Christian voters, the rest are merely lumped together as Protestant, so whether one is an Episcopalian lesbian, a Southern Baptist that hasn't attended church since child hood, or a Methodist Minister, if they still say that they are Christian, then they all are counted as "the Protestant vote".