That our defense industry had problems was evident when there wasn't enough steel around (of the correct grade and composition) to up-armour humvees. We aren't going to be able to import the stuff we need when the place we'd likely import it from is the same bunch we may be in conflict with.
This is another problem with closing mills, mines, and other facilities involved in resource extraction. Not to mention the skills lost when the workers move on, retire, or simply die of old age. Some things just can't be put on the shelf for later.