This recent New York Times article discusses how important gay marriage has become for conservatives, providing many conservative groups with a new focal point.
Indeed, gay marriage (or the specter of it) is probably a more important issue to conservatives than it is to liberals. For many liberals, the issue is relatively unimportant, compared with, say, war in Iraq, federal judiciary appointments, drilling in Alaska, and deprivation of civil liberties under the Patriot Act. Meanwhile, for many conservatives, gay marriage seems to be the most important issue. And that difference in relative importance influences how politicians approach the question.