Every penny paid in tariffs was paid by Americans. Period. The only way to avoid that added cost was to change supply chains. It takes years to move production and redesign products to use different components. Some of the supply chain collapses right now are due to this disturbance in moving supply chains out of China without enough capacity in place to pick it up.
No, that does not necessarily follow.
It only follows if there was no change in the aggregate price, or the aggregate demand, for the goods subject to the tariff.
Very simple example: assume that, ex ante, Buyer is willing to pay $100 for Good X, but is not willing to pay $120. Further assume that Seller's COGS for Good X is $80, so that Seller expects a pre-tariff profit of $20 on a sale.
Now assume that a tariff equal to 30% of the pre-tax price is imposed. The cost to Buyer will be $130 = $100 plus $30 tariff, which Buyer is not willing to pay.
One of two things will happen: the sale will not take place, in which case both parties are worse off, and in particular, Seller has lost a potential $20 profit. Alternatively, since Seller most likely already has significant sunk costs in producing/acquiring Good X, Seller will reduce the price so that Buyer is still willing to buy.
Assuming that Buyer is still willing, at the margin, to pay $119 for Good X. Seller will therefore be willing to reduce its price to $91 in order to make the sale. As a result, Buyer pays $119, Seller remits $28 to the government, and Seller retains a net profit of $11.
Thus, in this hypothetical, both Buyer and Seller have borne a portion of the cost of the tariff. Buyer has borne $19 of the tariff, and Seller has borne $9 of the tariff.
Even if goods are already in transit and pricing has been nailed down, depending on the relative bargaining positions of buyer and seller, the sales contract may have a taxes provision in it that allocates the burden of any additional taxes between the two parties.
So, no, it is not a categorical consequence of tariffs that the buyer - i.e., Americans in this case - always economically bear 100% of the cost of a tariff.
This econ lecture explains a little more about the differences between statutory incidence and economic incidence of a tax:
https://scholar.harvard.edu/files/stantcheva/files/lecture3.pdf