I’ll point this difference out between Rasmussen and the rest of the pack. As far as I know they are the only ones applying a likely voter screen on their presidential approval poll. Every other poll is either registered voters or adults. It’s not really an apples to apples comparison.
Rasmussen says 50% of likely voters approve of the job Trump is doing while Gallup says 41% of adults approve of the job Trump is doing. It is possible that they are both perfectly accurate since they are not answering the same question.