Trueman's group is now called the National Center on Sexual Exploitation, and he’s finding 2016 presidential candidates less eager to respond to a survey that includes questions about porn’s legal status alongside ones about prostitution, sex trafficking and child exploitation.

Of a GOP field that included more than a dozen candidates when the group released its survey in early November, just one – Santorum, a former Pennsylvania senator who withdrew from the race Wednesday after performing poorly in the Iowa caucuses – has responded.