Dems did way better with the economy than the previous two GOP presidents. If anything, Trump has managed (so far), not to screw it up. He's been a pretty ineffectual president, and is a weak candidate, IMO, the whole unhinged lying will come home to roost at some point.
His best chance is to declare a war before the election, get the country to line up behind him under the national pride mantra...
That said, never underestimate the Dems putting an even more terrible candidate out there... (ahem, Joe Biden).