I feel like I started hearing this around 2004 or so... But it really got attention around 2008.
I would agree with this. It didn't get much attention until 2008, but the signs were certainly there in 2004.
Karl Rove's strategy was to bring conservatives out to the polls by way of the Anti-Gay Marriage campaign and the "moral values" rhetoric. It proved to be just effective enough. Don't forget, however, that Bush did decently with Hispanics back in '04 and that may have been enough to be the difference in FL and in his NM win.