Many of the precision machine tools needed to build more machine tools to build stuff in factories were shipped overseas decades ago. There are things we are hard pressed to make, that you need to even be able to start to build a factory in the US. Can it be done? Sure. Is it expensive? Also sure. Not going to happen in 4 years. Not going to be cheap. Done wholesale with no regard for other economic forces at play, it seems like the kind of move more likely to shutter existing factories.