How might US trade policy backfire for its economy?

A CNN report says the U.S. government's tariff and trade policies hurt small businesses domestically. Dozens of leading economists in the U.S. have signed a public declaration warning that President Trump’s use of tariffs could trigger a self-inflicted recession. The International Monetary Fund predicts that U.S. growth will slow to 1.8 percent this year. How might US trade policy backfire for its economy？