You said literally the same thing he did.
Outbreaks should consider an exponential growth model with time-- at the current rate the number of cases is doubling every three days. If you assume that even 1% of the population gets it, a 0.7% mortality rate as you and Trump surmise, that's 20k+ Americans dead.
The numbers are staggering and shouldn't be simply thrown aside because of the single digit mortality rate. Yes, the elderly are more prone, but the mortality rate already has that factor built into it.
I would do some more research before dismissing this as you are.