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.
Trump tariffs
The Trump tariffs are a series of tariffs imposed during the presidency of Donald Trump as part of his economic policy. In January 2018, Trump imposed tariffs on solar panels and washing machines of 30 to 50 percent. Later the same year he imposed tariffs on steel (25%) and aluminum (10%) from most countries. On June 1, 2018, this was extended on the European Union, Canada, and Mexico. The only countries which remain exempted from the steel and aluminum tariffs are Australia and Argentina. Separately, on July 6, the Trump administration set a tariff of 25% on 818 categories of goods imported from China worth $50 billion.