I didn't say total self-sufficiency couldn't be done. I wasn't even saying it couldn't be done quickly.
If you're ok with going back to the Dark Ages, you could do it overnight. The US absolutely has the capability to become a completely self-sufficient medieval country right now. All you really need is food, water, wood, stone, and iron for that. We can handle that. 99.9% of us would be living in mud huts and dying of dysentery- but we could do it.
But if you want to maintain the lifestyle and modern benefits (technological, medical, etc) we enjoy now, and be completely self-sufficient as a country, that's a way, way more difficult task that would very likely involve serious disruption and violence.
After the dust settles from all the upheaval, THEN you could start building the infrastructure we don't have now and training a whole lot of people for new jobs. Don't forget though, one of the biggest challenges is going to be convincing a large percentage of the population that it's fun to work in factories.
Anyway, it's a pointless argument- we aren't going to stop trading with other countries, short of some kind of global collapse. Even then, I promise you we'd re-establish some kind of international trade again very quickly, because that's just how humans and economics work.
All this said, I personally think we rely TOO MUCH on international trade right now. While we can't realistically be completely self-sufficient, I absolutely think the US needs to bring a few strategic industries back on our own soil, and quickly.