Tariffs are only effective when they are so large that China or Mexico would be unable to pass the cost on to US consumers because their product would not be price competitive.
You take a $40,000 car coming in from Mexico and put a 25% tariff on it and price goes to $50,000 and nobody is going to buy
You take a $40,000 car coming in from Mexico and put a 25% tariff on it and price goes to $50,000 and nobody is going to buy