Presidential candidates are asked to sign pledges all the time, but the GOP primary has been roiled for the past few days by an uncommonly influential document -- the Marriage Vow: A Declaration of Dependence Upon Marriage and Family -- put out by an Iowa group, the Family Leader. [. . .] After losing in the primary, the fiercely anti-gay Vander Plaats led the successful campaign to oust three supreme court justices who had voted for the same-sex marriage decision. Now at the helm of the Family Leader, he has brought in presidential hopefuls for a speech series and is openly cultivating an image as Iowa kingmaker. I spoke with Vander Plaats by phone Monday night to check in on the developments surrounding the Marriage Vow and the presidential contest in Iowa. The following transcript of our conversation has been edited slightly for length. (Justin Elliott, “The man behind the marriage vow,” Salon, 12 July 2011) - - - - - - - - - - While our laws and customs are influe...