There's concern that if all our chips come from one country, they could cut the supply off and make demands. That's called an "embargo".

It's also done to protect local industries, hence the term "protectionism". For example, Canada's large tariffs on American milk are there to protect the local Canadian milk producers.

AFAIK, Trump's tariffs are meant to serve the following purposes:

1. so critical supplies, like chips, will be produced domestically

2. to raise money for the treasury

3. to convince countries that have high tariffs to lower them in exchange for the US to reciprocate in lowering ours

4. to incentivize foreign manufacturers to invest in factories in the US

5. to use them as a negotiating tool for other terms favorable to US interests

These are not crazy things. We'll see how things play out.

They’re not crazy goals, but the way these tariffs are being implemented does not further most of them.

3 and 5 are undermined by the fact that even nations with positive trade surpluses with the US, and countries like Japan with Trump first term negotiated trade treaties (which for Japan included major concessions already) are being hit with these tariffs.

1 and 4 are a problem because many of the inputs into building out US manufacturing capacity come from abroad and are hit by tariffs. Secondly many of the manufacturing inputs into making products in these factories would come from abroad and be tariffed, unless those supplies are bootstrapped domestically first but there is no policy to ensure this. Thirdly as soon as the tariffs go away, these factories would become uneconomical, so they are a gamble on that not happening in the lifetime of the factories.

Finally, who’s going to build and operate this huge new manufacturing sector? Infrastructure construction relies heavily on immigrant labour that’s being driven out, so does actual manufacturing, and there are no hordes of unemployed Americans lining up for manufacturing jobs. It’s addressing a problem that largely doesn’t exist, to build out less efficient more expensive ways to make stuff, in a way that can’t work anyway.

Manufacturing investment surged in the last few years with the introduction of the CHIPS and Inflation Reduction acts. It’s going to be hard to disentangle the continuing effects of that from the effects of the Tariffs, but it’s hard to see how the Tariffs can have a positive effect.