President Trump’s aggressive use of tariffs has secured overwhelming support among Republican voters, according to a new Economist/YouGov poll, cementing a dramatic transformation in conservative economic thinking that would have been unthinkable a generation ago. The survey, conducted Oct. 17-20, found that roughly two-thirds of Trump voters and Republicans support maintaining or increasing current tariff levels — a striking endorsement of trade policies that the party’s establishment once uniformly opposed. Among conservatives, 62 percent support maintaining or increasing current tariff levels. Even more remarkably, 59 percent of Trump voters back imposing a 100 percent tariff on all goods imported from...