Rasmussen Polling leans fairly heavily Republican, so Trump quotes them all the time. (Two months ago, when all other polls had Trump around 39-42% approval, they had his approval at 50%, and it's hovered near there since, though has been lowering.) But their new tracking poll just released has his approval plummeted all the way down to 43%. And his disapproval up to 55% -- with "strongly disapprove" at 46%, which is even higher than his approval.
Beyond the specific numbers, though, what's the most important thing (and generally so with any poll) is the trend, since specific numbers have their margin of error. And the trend here is not only downward but significantly so. And most importantly, for the right-leading Rasmussen.