Tariff
A tariff is called an optimal tariff if it's set to maximize the welfare of the country imposing the tariff. It is a tariff derived by the intersection between the "trade indifference curve" of that country and the offer curve of another country. In this case, the welfare of the other country grows worse simultaneously, thus the policy is a kind of "beggar thy neighbor policy". If the offer curve of the other country is a line through the origin point, the original country is in the "condition of a small country", so any tariff worsens the welfare of the original country.
Walker tariff
The Walker Tariff was a set of tariff rates adopted by the United States in 1846. The Walker Tariff was enacted by the Democrats, and made substantial cuts in the high rates of the "Black Tariff" of 1842, enacted by the Whigs. It was based on a report by Secretary of the Treasury Robert J. Walker. The Walker Tariff reduced tariff rates from 32% to 25%; it coincided with Britain's repeal of the Corn Laws and led to an increase in trade. It was one of the lowest tariffs in American history.