U.S. stock-index benchmarks on Wednesday opened firmly lower, set to close in the red for the first time in five sessions after the Trump administration said it would place tariffs on a further $200 billion in Chinese goods, escalating tensions between trading partners in Washington and in other parts of the globe. The Dow Jones Industrial Average fell 166 points, or 0.7%, at 24,758, the S&P 500 index declined by 0.5% at 2,778. Meanwhile, the Nasdaq Composite Index fell 0.7% at 7,708. All three benchmarks had enjoyed four straight days of gains as trade fears had taken a back seat to better economic reports, notable Friday’s better-than-expected jobs report for June, and coming second-quarter earnings, which are expected to be strong. In economic reports, the June producer-price index rose 0.3%, as did the core PPI, which excludes volatile food and energy. In corporate news, shares of industrials and materials stocks, the most vulnerable to trade spats, were lower. Among notable stocks, Boeing Co. fell 1.6%, shares of 3M Co. were off 1.2% and Caterpillar Inc.’s shares were 2.1% lower, in early morning trade Tuesday.