And how does that make american IT companies with datacenters, etc, more competitive?

In the short term, chips would just be 5-20% more expensive in the US compared to anywhere else. They'd need to raise the tariffs a bit more, though, to make sure there's incentive to increase production to a level that can satisfy demand.

In the long term, it would provide the US with an independent source of chips, and eventually allow them to let go of any plants to protect Taiwan from China.

You haven't answered: how do american datacenters stay competitive?

In Europe or Japan I can already build much cheaper, workforce is cheaper, now even hardware is cheaper.

How does data centers in US stay competitive? Why would Google or others build their new AI infrastructure in Ohio rather than elsewhere?