Apparently, he's not smart enough to realize that the memo is self contradictory, in that it starts off with the premise that the investigation is somehow tainted because it started with information that had passed through a Democrats hands. Assumption there is that no Democrat can possibly tell the truth, plus that even if it was true, it should be ignored because it came from a Democrat.
That foolishness aside, the memo also tries to smear the agent who started the investigation IN JULY, months before the FBI got the Steele dossier.
So either Trump is flat out stupid, didn't bother to read it, or he figures the base is that stupid. Pick one or both or all three for that matter.