The overwhelming majority of imports come from Canada, Mexico, Japan, Korea, Brazil, Germany. All of whom are, at least for now, strong allies of the U.S. I don't see where that poses a national security threat to the U.S.
f Canada and Mexico want exceptions, fine, let them each negotiate whatever deal they can instead of pretending that the NAFTA scam was carved in stone by God Himself.
And you number for aluminum is way off : Just one of many articles explaining the import/export of steel and aluminum. Notice that aluminum imports are 60% of the US market, much worse than the situation in steel.