Since the 2004 presidential election, Democrats and Republicans have operated on the assumption that one of the reasons for the Bush victory is the massive size of the Religious Right. Religious conservatives have spent the year pressing for legislative victories, such as confirmation of Bush's judicidal nominees, to reward them for their clout. Democrats have been debating internally whether they should be less secular.

But a new look at Beliefnet's popular "Twelve Tribes" analysis shows something surprising: the religious left is just about the same size as the religious right.

This is one of the most intriguing findings surfacing from the new data that's part of Beliefnet's "Twelve Tribes of American Politics," a typology created last year by combining data about religious affiliation, practice, and political affiliation. These groups cut across old denominational boundaries, and often have unique relevance to U.S. politics, in terms of how they vote and the issues that are most important to them.

The rise of the Religious Left was a major factor in the 2004 election:

The Religious Left made up 14 percent of the electorate, an increase from 11 percent in 2000. By comparison 15% came from the "Religious Right."

69% of this group voted, compared to 51% percent in 2000 (and 69% of the religious right.)

21% of John Kerry's votes came from the Religious Left, not that much less percentage-wise than the 26% of Bush's votes that came from the Religious Right.

What caused the religious left to turn out for Kerry in record numbers? Opposition to the Iraq war.

The political awakening of the Religious Left carries several implications for the Democratic Party. For one thing, Democratic leaders cannot view the party as primarily secular. Add up the numbers of the Religious Left, Democratic-voting Latino Christians, Black Protestants, and the modest support from conservative Christians and you have 52% of Kerry's vote. Secular voters did vote in record numbers for Kerry but only accounted for 16% percent of his vote.

More worrisome for Democrats is the fact that Kerry lost in spite of record mobilization of the Religious Left.

Was that because the Left was out-hustled by the Religious Right? In part. Bush did do well among the most conservative religious voters, increasing turnout from 62% to 69%. But the share of the total Bush vote from the Religious Right actually declined slightly (from 16% in 2000 to 15%).

But where Bush showed the most improvement was among the "Heartland Culture Warriors," mainline Protestants and Catholics with traditional beliefs and practices. In 2000, Bush won 66% of the Heartland vote; in 2004 he won 72%. Turnout was also up for this group.

The Heartland Culture Warriors viewed social issues as the most important. In other words, Bush's positions on gay marriage and abortion likely helped him even more with this group than the Religious Right.

These social issues also helped Bush make some gains among the more traditional Latino and black churches.

But the economy was critical to the black Protestants and members of other minority faiths who voted for Kerry. Indeed, Kerry did well among many of the Twelve Tribes for whom the economy was top priority.

Kerry may well have lost the close contest among the "Convertible Catholics," white Catholics with moderate beliefs and practices. Earlier in the campaign, Kerry led in this swing group. But Bush edged out Kerry, 55% to 45%, on the basis of foreign policy concerns.

Clearly, Democrats who are planning a comeback for 2008 or in the 2006 congressional elections need to absorb both the impact of the Religious Left and the devastating effect of having lost the moderate Catholic vote. It will be very hard for a Democrat to win without realizing that a big chunk of the party is not secular.