When Xi Jinping took the reins of a booming China two years ago, President Barack Obama saw an opportunity to remake America’s relationship with the Asian power. But even after Obama’s unusually robust efforts to forge personal ties with Xi, the two leaders are meeting in Beijing amid significant tensions, both old and new. Xi has consolidated power since taking office, deepened China’s provocative maritime disputes with its neighbors and stands accused of continuing cyberattacks against the United States. U.S. officials have new concerns over the potential for a crackdown on pro-democracy protesters in Hong Kong and are warily watching...