Tariffs on imports from Mexico are a tax on U.S. citizens.

If President Trump wants Mexico to pay for The Wall, he can not do it by putting a tariff on imports from Mexico to the U.S.  A tariff on imports is a tax paid for by U.S. consumers in the form of higher prices.  If the tariff stops the imports, it will allow the higher prices to be charged for U.S. made products.  It will be a “win” for the company and its workers who get the protection, but it will be paid for by U.S. citizens, not Mexico.