Let’s do a hypothetical. Let’s say Wal-Mart buys $100 million worth of toilet brushes. They mark it up 50% (typical retail mark-up) and sell them for $150 million, of which $10 million is profit. So they make10% profit on their $100 million (typical retail profit margin).
100% tariffs are imposed and so Wal-Mart buys half as many brushes for the same $100 million. They mark them up to $150 million, and again make $10 million or 10% profit.
But note, they only sold half as many, which means they had to sell each brush for twice as much to make both the same dollar amount profit and percent profit.