If wikipedia is to be believed, we might not be as far off as you'd think. One third of our pharmaceutical consumption is already domestically supplied, and the amount we export amounts to about 40% of our consumption. Put the two together, and suddenly there's 70% of our needs already met. Imports from non-us suppliers should be able to fill the gap while domestic production is ramped up.

Now obviously reality is going to be far more complex than this napkin math, but I'm just pointing out that our domestic production is not starting from zero, and is already at the scale where supplying our own relatively small market is not out of the question.

It's not just building the factories. The FDA has to minutely inspect the factory and it's procedures, and give it's approval before they can sell anything made there. It takes time for that to happen, especially with the RIFs they're pushing through (which is relevant because they also re-inspect the factories every ... ?5? years and they're having problems keeping up with the current batch of factories).