Do you think America's farmers will continue to support their conman president? No position worse to be in than thinking he's with you.
American consumers will be asked to pay for the import tariffs/ pass through costs. American farmers (and others) will be unable to sell their products in China due to the Chinese government's inevitable response.
And because the US is no one's friend these days, the rest of the world will lean more towards China than they might have done with other presidents.
http://www.bbc.co.uk/news/business-48210313