We tend to think of the campaign battles as being the quest for those on the middle of the political spectrum. But there’s another place candidates forage. The very Republican and very Democratic groups nonetheless have dissenters in their midst.

For instance, in 2004, 20% of the Religious Right were Democrats, and 31% of the Religious Left were Republican, according to the Twelve Tribes study. These dissenters sometimes found themselves in an awkward situation: they were voting one way while their peers and spiritual kindred spirits were voting a different way. This makes them a ripe target because the power of peer-pressure can help solidify key party constituencies.

We saw this happen in the Republican party from 2000 to 2004. Republicans saw a steady movement of dissenters switching to the majority view of their group. For instance, in 2000 the Republicans won 62% of the Heartland Conservatives. In 2004, they won 72%. In 2000, 84% of Religious Right voters went Republican. In 2004, 88% did. That’s a lot of votes

According to the new Twelve Tribe study, we’ve seen a similar consolidation on the Democratic side.

Percent identifying as Democrats in the summer of 2008:

• Religious Left: 2004: 51%, 2008: 63%
• Spiritual Not Religious: 2004: 51%, 2008: 63%
• Latinos: 2004: 54%, 2008: 62%
• Muslims and others: 55%, 2008: 69%
• African Americans: 2004: 71%, 2008: 83%

Meanwhile, the most conservative groups have remained just as Republican but don’t have much room to go a whole lot higher.

In all, this means the Tribes have become more polarized by party, with seven clearly leaning Democratic, two massively favoring Republicans, and three straddling the middle (moderate evangelicals, whitebread protestants, convertible Catholics)

(More on the Twelve Tribes here)