Rasmussen is noted for its right-leaning bias, so it's not surprising that you would rely on them for Trump's approval. They are an outlier, not a mainstream poll. Despite their boast that they were the only ones right in 2016, they were not the only ones polling Trump and Clinton in a near dead-heat at the end. Everyone from Gallup to 538 to Pew had it a close race after Comey's letter.
Despite that, Rasmussen - even Rasmussen, the poll Cons hang their hat on! - has Trump's approval rating down from his election.
When he took office, his approval rating was 56%. Today, it stands at 51%
What's gone up is Trump's Disapproval rating, which was at 44% when he took office and is at 47% now.
Rasmussen Approval Index History
So, Trump's approval rating
has fallen since the election, according to the most biased poll in his favor out there.
What's next?