Trump “Orders” US Firms To Exit China, Can He Do that?

Twitter post by @realDonaldTrump: ...unfair Trading Relationship. China should not have put new Tariffs on 75 BILLION DOLLARS of United States product (politically motivated!). Starting on October 1st, the 250 BILLION DOLLARS of goods and products from China, currently being taxed at 25%, will be taxed at 30%...Image result for Our great American companies are hereby ordered to immediately start looking for an alternative to China

Can he order US companies to do anything? No. Has he considered what the world for US companies would look like if they stopped buying foreign goods and foreigners stopped buying US companies goods?