The improving economy helps the GOP, generally, I would agree, as they happen to be in office right now as it improves. It should help them in the mid terms.
As to 2020, the question will be how much of this growth shows up in middle American pay checks. A one time bonus isn't going to do the trick, especially if it was two plus years after the last election cycle.
If the numbers translate to higher wages, then yes, it will help Trump. If wage rates remain stagnant for the middle class, then it will hurt because the Dems will be in a position to argue that the tax breaks favored the wealthy.
Personally, I think you'd still have seen a lot of growth at this point, regardless of who won. If you think it was tax cuts, then that probably would have been the case for Kasich, or Rubio, too.