There are regulatory hurdles to making a manufacturing plant in the US however: minimum wage, safety regulations, etc. etc. So it will be more expensive if made in the USA.
Alternatively, things can become like the Car industry. Where certain parts are manufactured outside the US, while the final car is manufactured inside of the US. Toyota has a major presence in the US.
I'm not saying I necessarily agree with it, but it helps to understand at least why Trump's supporters support Trump.