Biarritz, Aug. 25 -- President Donald Trump is threatening to use the emergency authority granted by a powerful but obscure federal law to make good on his tweeted "order" to U.S. businesses to cut ties in China amid a spiraling trade war between the two nations.

China's announcement Friday that it was raising tariffs on $75 billion in U.S. imports sent Trump into a rage and White House aides scrambling for a response.

Trump fired off on Twitter, declaring American companies "are hereby ordered to immediately start looking for an alternative to China." He later clarified that he was threatening to make use of the International Emergency Economic Powers Act in the trade war, raising questions about the wisdom and propriety of making the ...