Economists will tell you that the US President has very little effect on the economy. That goes for all the good stuff as well as the bad stuff. Sure, he has a role in passing budget legislation, and the current President just did sign a new tax bill, but economists generally don't see it doing much for growth (while they expect it to expand the deficit in the long-term -- see below).http://www.igmchicago.org/surveys/tax-reform-2
I think it's safe to say that the Chair of the Federal Reserve, now Jerome Powell, has a much larger role in the economy than the President. Then there are other factors that no American policymaker is responsible for, of course. OPEC jacked up oil prices during Carter, for instance. The tech boom coincided with Clinton. The worst financial crisis in 70 years happened late in GW Bush's second term. You get the point.
As an aside... The original post highlighted low unemployment among blacks, and this seems to be a meme going around the conservative media of late. I think the subtle message is clear: black people are actually doing great under Trump, and need to stop complaining. Well, keep in mind that the unemployment rate is still much higher for blacks than it is for whites, and other metrics such as net wealth, home ownership, etc. are still much worse. The point is, don't look at this single number as an indicator of economic well-being.