US President Donald Trump's reliance on tariffs rather than sanctions has been described as both the "world's worst bet" and "a powerful proven source of leverage" to protect the national interests of the United States. While tariffs essentially are taxes on imports to protect domestic industries, sanctions are penalties imposed on other countries to punish or influence their governments. Sanctions typically put restrictions on trade or finance. Since his return to the White House in January, Trump's tariff threats against dozens of countries have created great uncertainty among US businesses and global trading partners. What's become known as "tariff tango" — bold pledges of steep duties on foreign goods, followed by abrupt reversals — suits Trump's shifting political or economic goals. Yet, financial markets remain on edge, not knowing how or when the president may deploy tariffs next. The tariff on China, the biggest economic and military rival to the US, reached historic highs in April, soaring to 145% before being significantly cut the following month after trade talks in London. Trump's sudden increase and later rollback of tariffs show how he uses them as a flexible way to fix what he sees as unfair trade, based on past trade disputes. "What shapes the president's views is the rapid rise of Japan in the 1980s, and the feeling that the Japanese were out-competing the iconic American car industry because the US has been too generous in its trade terms," Jennifer Burns, associate professor of history at Stanford University,