The United States and China escalated their acrimonious trade war on Thursday, implementing punitive 25 percent tariffs on $16 billion worth of each other's goods, even as mid-level officials from both sides resumed talks in Washington. As David Pollard reports, the world's two largest economies have now slapped tit-for-tat tariffs on a combined $100 billion of products since early July, adding to risks to global economic growth.