Trump's tariff threats on Canada, Mexico will be "very bad for US, world". How will it impact American economy?

Trump's tariff threats: President Donald Trump has threatened to impose a 25% across-the-board tariff on all imports from Canada and Mexico on 1 February. The tariffs and trade war will probably cause many businesses to reduce their planned investments, and that, economists say, will hurt economies worldwide. Trump insists that his aggressive trade policies will be a win-win for Americans but experts have said this will hurt the US economy, workers and farmers.