Think of it this way. A new coach is hired onto a basketball team. At the time the coach is hired on, the basketball team is shooting 75%. Years later, under the same coach, after extensive practice and coaching, the team now shoots 88%. That coach leaves, and a new coach comes on. During the first couple of months following the first coach's routine, the team improves from 88% to 90%, and the new coach just sits on the bench going "Yeah team, go! Do what you were doing, I'm going to sit here and be a fatass and do nothing." Sure, the team is shooting 90%, but who actually did the work, the first coach who brought that average up, or the second one who took credit for it while not actually contributing anything?
It doesn't take a genius to understand that just because unemployment is low under Trump, doesn't mean that he actually did anything to cause it to be like that.