Most Conservatives will not participate in any polls associated with left wing organizations. Many know that Rasmussen is a neutral organization and are willing to participate in their polls. I think that this helps explain the discrepancy. Rasmussen currently shows President Trump with a 51% approval rating.
The last I checked Rasmussen had the Dems with only 3 percent generic lead as of October 31 and for the period ending October 25, 43% surveyed see the country heading in the right direction versus 53% saying it is on the wrong track, a gap of minus 10. At about this time in 2010, it was 32% saying on right track versus 64% saying on wrong, a gap of minus 32.