That is, from one perspective, the coalition is just a matter of political opportunism. If your primary concern is the deficit, for example, you might not care that much about gay marriage; if you're ardently pro-life, you may vote on abortion rather than taxes. And to be sure, I think this is part of the story; you can certainly find a lot of Republicans who are more concerned with one set of issues rather than the other, and I talked to some of those types in Fort Worth (including some libertarian-type tea party members).
However, a lot of Americans describe themselves as conservative on both economic and social issues--31%, according to a recent Gallup poll--so I wanted to ask them whether that's more than just coincidence. I wrote up some of the conclusions at Democracy in America.
There's something else to add here. I've been going through a lot of poll numbers lately for both Texas and the nation as a whole, trying to figure out to what extent Texas is really an outlier on social issues. What I've found is that this "about a third" figure is remarkably consistent, both in Texas and around the country, on a variety of issues.
With regard to gay marriage, for example, it's pretty clear that a substantial majority of Americans supports legal recognition for same-sex couples, and about a third are against it, although the size of the majority in favour depends on whether you're asking strictly about marriage or including civil unions as an option. Last month, for example, a NY Times/CBS Poll found 38% of respondents supporting gay marriage, 24% supporting civil unions, and 33% against both. In Texas, according to a February 2012 survey from the Texas Politics Project, the split was 31% supporting marriage, 29% supporting civil unions, and 33% against both. The most confusing poll results are on abortion--it again depends on how the question is framed--but in both Texas and the United States as a whole, you have a minority that is strongly pro-choice, a smaller minority against abortion in every case, and a lot of people in the middle who are apparently uncomfortable with abortion but think it's okay in certain circumstances. (Oddly, on that question, Texas actually looks a little more liberal than the country as a whole, but this might be a quirk of the way the respective questions were worded). As far as the 'war on contraception, this year Public Policy Polling found that 37% of Americans were opposed to the idea that the government should require employers to cover contraception as part of their health insurance offerings. (Similarly, 38% of Texans supported Rick Perry's decision to defund Planned Parenthood.)
On the more general question of church-state separation, a national survey from the First Amendment Center found 67% of Americans agreeing that the First Amendment requires the separation of church and state. Relatedly, a 2010 survey from the Pew Research Center’s Forum on Religion & Public Life found 68% know that the Constitution establishes the separation of church and state. (In 2010, the Texas Freedom Network found that 68% of likely Texan voters agreed that separation of church and state is a foundational Constitutional principle.)
On balance, it seems pretty clear that in both Texas and the United States, social conservatives (or religious conservatives, if you prefer) are the minority. That's why they don't usually win on the issues: abortion is legal, contraception is widely available, and gay marriage is progressing through the states. They are, however, a sizeable minority--and more to the point, an organized and voluble one. Their strength is in their devotion rather than their numbers.