President Trump’s economic conflict with China is set to escalate this week, as the administration plans to unveil fresh tariffs on $200 billion in Chinese products entering the U.S. and Beijing debates new ways to retaliate against U.S. corporations doing business in China.

The threats from both sides of the Pacific risk upending a fragile new diplomatic initiative—led by Treasury Secretary Steven Mnuchin and supported by top U.S. financial and business executives—to see if they can broker negotiations aimed at staving off...