That’s pretty much the bottom line in Nate Silver’s regression analysis
of the impact of 23 demographic factors on partisan voting in the 2008
election. His object was to see how much of a difference union
membership makes to the likelihood of voting Democratic. The answer is:
in the same ballpark as evangelicals and weekly worship attenders (God
gap) were likely to vote Republican.

Of course, the relative impact of these demographic preferences varied,
because the size of each group varies About 10 percent of 2008 voters
were union members. Roughly a quarter were evangelicals. And nearly a
half were weekly attenders. Silver calculates that the union vote
boosted Obama’s (and the Democratic congressional) total by 1.2 percent.
Do the arithmetic and that means a three percent boost from
evangelicals and a six percent boost from weekly attenders for the GOP.
Look for both of those numbers to increase in 2012.