I don't dispute that, but it's not what I was referring to. Some polls ask what people think of the president (favorability ratings), and some are more specifically geared to asking about the job the president is doing (approval ratings). The article I linked to from Gallup points to situations where they do not always correlate as you would expect. For example, Bill Clinton in 1993 and 2000. In 1993 he had 59% favorability and 49% approval,and that just about reverse by 2000 when he had 60% approval, but only 46% favorability. People disliked him after the scandal, but they also conceded he was doing a good job.

So, what I wonder is what questions are actually asked regarding candidates? There isn't any data on them doing the job itself yet (unless they are an incumbent, which none are this cycle), so are they asking about how much they like the person, like the policies, or how confident they are the candidate can perform well? The answer to that question may lead to different likely reasons for the question at hand. Sanders is a likable guy. I like him. I'm also not convinced his policies, as expressed on the campaign trail, are feasible. Conversely, Hillary Clinton isn't very likable. I don't really like her. I do agree with many (but not all) of her policies, but most importantly I think her policies are feasible and have a chance of being implemented if she's elected. I am, in fact, the exact sort of person that might have expressed a favorable opinion for Sanders but voted for Hillary.