U.S. stock futures pointed to a slight rebound for Wall Street on Tuesday and global stocks were mixed as the U.S. and China, the world's two largest economies, escalate the rhetoric and retaliation in their trade war. China's retaliatory tariffs on $60 billion worth of U.S. imports sent markets reeling Monday, with the Dow Jones Industrial Average plunging 617 points, or 2.38%, to a three-month low and the S&P 500 giving back 69.5 points to take its decline since Donald Trump first threatened tariffs on May 5 to 4.5%.