YJ, you're reading the Rasmussen poll wrong. 42% is not the overal job approval of Obama. It's the number that "strongly disapprove" of Obama's performance. Rasmussen does this thing where he breaks up the approval and disapproval of the President's performance into "strongly approve", "somewhat approve", "somewhat disapprove", "strongly disapprove". Rasmussen isn't the first pollster to do this, but I still feel it's redundant and kind of meaningless.
Because it's so meaningless, it's silly to see Rasmussen considering these results to be the headline results. The real important part of the Rasmussen poll results is always buried several paragraphs in the Rasmussen article. That would be Obama's actual job approval/disapproval rating. (Approval being the number who "strongly approve" + those who "somewhat approve" .)
That number, according to your Rasmussen link, is... 46% approve, 53% disapprove.