

It takes 7+ years to bring a new factory online. more to get all the kinks worked out and at full production
Not to take away from your point but they also have to
- make sure product is at par with the previous alternative in terms of quality
- make sure your supply chain is willing to shift to your new product
- have a healthy supply of workers OR
- have good automation in their production line (automation supply should also be sourced from within the country)
Once you have created this factory (which needs to be subsidized by the government in order to compete with the foreign product), we then apply targeted tariffs so that people can slowly shift to the homegrown product. Doing all this can takes decades of careful planning.
Tariff is not an ON/OFF switch which Trump thinks
Now you know why your mom spent so much time with the Amiga