BEIJING: Terry Branstad, Donald Trump\u2019s pick for ambassador to China, has close ties both to the U.S. president-elect and to Chinese President Xi Jinping. He\u2019s going to need them.\r\nThe 70-year-old Mr. Branstad, who first met Mr. Xi in 1984, is a six-term governor with little obvious experience in foreign diplomacy. He will land in Beijing at a time when the U.S.-China relationship is increasingly fraught.\r\nMr. Trump has threatened trade sanctions against China as soon as he takes office. He further roiled the waters by speaking by phone last week with Tsai Ing-wen, the president of Taiwan, which China considers a breakaway province and has sought to isolate on the world stage.\r\nOther flashpoints include Beijing\u2019s military buildup in the South China Sea, cybersecurity and complaints from U.S. firms that regulatory barriers are helping to keep them out of the Chinese market, even as Chinese companies have aggressively sought acquisitions abroad and in the U.S.\r\nUnder President Barack Obama, U.S.-China leadership on combating climate change offered a rare bright spot in the relationship. Such cooperation looks significantly less likely now, as Mr. Trump has said he would pull the U.S. out of the Paris climate accords and has chosen a climate skeptic, Oklahoma Attorney General Scott Pruitt, to lead the Environmental Protection Agency.