However the point really is, do there really need to be issues at the border when flights land? I guess you could exempt travellers so that there is the appearance of normality to people IRL, but that wouldn't prevent issues at the border for packages, and most people get a lot more packages than they do fly in/out of the US, so I'd imagine it wouldn't take long for people to really notice the impact directly (let alone several steps removed as companies can no longer import effectively).
Or not! But I don't think the problem is that we cannot craft regulation, it's whether we ought to.
On the other hand, that point is not as legitimate in the US as in Europe due to domestic companies such as Amazon that don't act in good faith. Stores that pretend to be marketplaces and therefore try to avoid responsibility for the stuff they sell for their subcontractors.
It could easily turn into your most expensive bag ever.
All food items simply _must_ be declared. There's two lines, so join the "something to declare" one. You'll be waved through after a quick inspection, or asked to surrender any offending items. Super easy. The declare line is often quicker as well.
I think you could adjust the rule so that it covered this situation, but didn’t cover shippers who specifically created fast shipping to avoid tarriffs and keep the processing outside the country.
That being said, I benefited from this when I ordered my Prusa 3d printer and I believe it was purposely priced exactly under the threshhold so that I would avoid the tarriff.
You could make being subject to the tariff depend on the shipper volume of course.