William McKinley was a member of the Republican Party. During the late nineteenth century, Republicans strongly supported tariffs to protect growing industries within the United States from foreign competition. The McKinley Tariff was passed into law in 1890, and it dramatically increased the tax rate on foreign products. While many business owners supported this legislation, American consumers generally opposed it, as prices increased for goods. During the late 1800s and early 1900s, the Republican Party and the Democratic Party continuously battled over tariffs. American opposition to the McKinley Tariff was so high that President Benjamin Harrison, a Republican, may have lost reelection in 1892 partly because of his support for the tax.
via Tax History Lesson: The McKinley Tariff | Tax Foundation
According to the Tax Foundation model, the tariffs planned and imposed so far by the Trump administration would reduce long-run GDP by 0.21 percent ($52 billion) and wages by 0.13 percent and eliminate 161,751 full-time equivalent jobs. If the Trump administration acts on threats to place new tariffs on automobiles and parts and additional tariffs on products from China, GDP would fall by an additional 0.45 percent ($112 billion), resulting in 0.29 percent lower wages and 347,988 fewer full-time equivalent jobs.
Other countries have announced intentions to impose tariffs on U.S. exports. If these tariffs are fully imposed, we estimate that U.S. GDP would fall another 0.09 percent ($23.5 billion) and cost an additional 72,864 full-time equivalent jobs.
via Tracking the Economic Impact of Tariffs | China Tariffs | Trade Tensions