Scary, but logical: Political Victory: From Here to Maternity
In states where Bush won a popular majority in 2000, the average woman bears 2.11 children in her lifetime — which is enough to replace the population. In states where Gore won a majority of votes in 2000, the average woman bears 1.89 children, which is not enough to avoid population decline.
It makes sense. If religious fundamentalists have more kids than everyone else, after a while there will be more religious fundamentalists than anyone else. With the human population already over 6 billion, starting a population growth war seems like a bad idea (read: recipe for extinction, or at least mass famine). That’s a big-picture problem, and one that is not easily dealt with.