Your characterization of the YouGov Emancipation Proclamation poll question is not as bad as those that emerged when it was first publicized; but it still gets key things wrong. The question was asked after a lot of prodding about opinions about Obama and then about executive orders, and only then did YG ask if respondents disapproved of specific executive orders. The EP was not named, either, just described. 5% of liberals and even 5% of blacks also disapproved of this unnamed executive order in this context.

http://otford.tumblr.com/post/140004086023/donald-trump-supporters-and-slavery