Under Trump and the republicans, the U.S. deficit has greatly increased and is in the ~$1 trillion dollar range. And unlike the deficits under Obama (where the U.S. was in a recession), the Republican deficit is occurring at a time when the U.S. economy is supposed to be growing.
Regulations to prevent another 2008/2009 meltdown are being removed, possibly allowing another 'bubble'.
The U.S. is not building up its infrastructure; many bridges need replacement. And the current focus of the Trump administration is on old (and rapidly becoming obsolete) areas of the economy... fossil fuels, manufacturing, etc. instead of technology.
Things may LOOK good now, but its basically a coat of paint on a termite-infested house, and the owners seem to have no interest in getting rid of the infestation.
Even after Trump leaves office, the effects of his administration will continue to be felt for decades.