It really depends on what Trump means by " built in the US". It won’t be that big of a jump if Apple is just assembling them there. If every component has to come from the US it’s likely impossible.

Apple is vertically integrated in a way many companies are not. It would be bad for them for sure but they already have really high profit margins. They could eat the cost and assemble in the US, but they won’t because they are already a velban good.