If the latter happens, will a domestic company come in and undercut the international sellers?
There needs to exist a domestic supplier to be able to fill the gap. My guess is that for many products, there simply isn't one.
Now we have no trade and a drop in demand for US currency.
This is painting the bullseye around the arrow - while this was entirely predictable, when did anyone in the administration state that this[1] was the goal? This goal is obviously is contrary to another stated policy goal of lowering inflation.
1. Initially, the stated goal was to make trade imbalances "fair"
Trade hasn't been this fair to the US since before WWII.
Hanlon's Razor suggests that your statement is incorrect.
Tariffs need consistency and stability to be effective rather than purely disruptive.
You can see this in how much more effective the countries applying tariffs against the US are handling things. Since they are applying tariffs and leaving them in place, the incentives are working properly, and they are disconnecting from the US businesses.
In the US, by contrast, businesses are either shutting down or holding their breath in the hopes that tariffs will pass.
Also the fact sheet[0] uses a paper which found a reduction in trade with China as evidence for why they should do this which I think is evidence enough that they are hoping for at least a modest reduction in trade "A 2023 report by the U.S. International Trade Commission that analyzed the effects of Section 232 and 301 tariffs on more than $300 billion of U.S. imports found that the tariffs reduced imports from China and effectively stimulated more U.S. production of the tariffed goods, with very minor effects on prices."
[0]: https://www.whitehouse.gov/fact-sheets/2025/04/fact-sheet-pr...
It doesn't matter to someone getting the pointy end of the stick whether it happened out of malice or stupidity--the pointy end still hurts.