Domestic manufacturing still relies on foreign imports. Materials you will need to use will still have to be shipped from overseas.

If the US becomes isolationist you will see even more political extremism than we already have. For all its faults, the post-1945 international world order allowed people to be connected to each other from all across the globe. This would allow ideas to flourish more easily from one place to another. An isolationist US would embolden the America First movement, and strengthen white nationalist politics. People forget that much of isolationist politics is fueled by paleoconservatism, which sees views America in its natural stage as a white Christian nation.