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I see part of the issue being that the Catholic Church let themselves become available to lobbying itself. Their messages are less concise as infighting goes on while the Pope grows older, causing their decrees to often become contradictive on issues. With a crop of fairly liberal Christians and Catholics to contrast the fundamentalist, we're seeing a generation of politicians that pick and chose their own value system, so of course that's going to threaten the fundamentalist Christian special interest groups who have redefined themselves in the last ten years. For the real answer to your question you need to look at what's happening within the Christian community itself (and then to a lesser degree, the radical left, as it starts to embrace issues on a morality level). Increasingly it's the concept of "values" treated as it's own platform that every single candidate in an election must face. instead of a social stance on a per issue basis. You can't go into a voting booth the way my Grandparents used to, with their union card, and just check off all the Democrat sponsored candidates and initiatives, so the new version of this is to align yourself with a different club. Remember that a good amount of Religious Americans pay ties to their Church. A good deal of our social programs are tied to religious organizations, and it builds an incredible loyalty even beyond the stereotypical idea of a bible thumper voter. I'm sure from their perspective it's the opposite... that you can't look at a guy like Ted Kennedy and think "well he's a good Catholic boy, it's safe to vote for him, he'll agree with me on abortion".
Even the blanket of religious fundamentalism has splintered to mean various things, which just makes these communities that much more aggressive in positioning themselves to push an agenda. The Christian community puts great energy in a whole variety of charities, but how many get them bombing buildings, and foaming at the mouth? The contradiction of their own values and actions has always existed, and just grows far more public as you see these groups "modernize". Meanwhile, politicians are equally to blame as they embrace and add credibility to moral call issues on a pick and chose basis where saving stem cells, and saving Iraqi lives are put on the same level.