U.S. President Richard Nixon shakes hands with Communist Chinese leader Mao Tse-Tung during Nixon's historic trip to China on February 21, 1972 in Peking. (AP Photo)

Chinese Vice Premier Li Lanqing , left, plays table tennis with former U.S. Secretary of State Henry Kissinger, right, at the Diaoyutai State Guesthouse in Beijing on Sunday, March 18, 2001. A grand reception was hosted here to mark the 30th anniversary of the historic "ping-pong diplomacy" in the China-U.S. relations. (AP photo/ Yao Dawei, Xinhua)

U.S. Secretary of State Henry Kissinger, left, and people?s republican of China premier Chou-En-Lai drink a toast at the end of a state banquet in the Great Hall in Beijing on Saturday, Nov. 10, 1973. (AP Photo/HWG)

FILE - In this Jan. 30, 1979, file photo, President Jimmy Carter and Chinese Vice Premier Teng Hsiao-ping hold hands outside the Oval Office of the White House in Washington as they met for the third time in two days for talks. (AP Photo/File)

U.S. Vice President George Bush shakes hand with a worker at Pepsi Cola plant in China's Shenzhen Special Economic Zone, Oct. 18, 1985 on the last stop of his six-day China tour. At center is Bush's wife Barbara. (AP Photo/Neal Ulevich)

FILE - In this Saturday, Feb. 25, 1989, file photo, China's Premier Li Pang, left, watches U.S. President George H.W. Bush, try out one of two new "Flying Pigeon" bikes presented by Pang, left, for the President and the First Lady in Beijing. (AP Photo/Doug Mills, File)

U.S. President George W. Bush holds Chou Ailing, 3 as he arrives for services at the Chongwenmen Protestant Church, Sunday, Feb. 26, 1989 in Beijing. (AP Photo/Scott Applewhite)

U.S. President Bill Clinton, first Lady Hillary Rodham Clinton, and daughter Chelsea laugh as they stroll along a section of the Great Wall of China in Mutianyu. The Clinton's also visted the Forbidden City in Beijing earlier in the day. (AP Photo/Greg Gibson)

President Clinton greets students at a school in Xia He, China following a speech Friday, June 26, 1998. Clinton held a roundtable discussion with villagers from Xia He earlier in the day. (AP Photo/Greg Gibson)

Chinese President Xi Jinping, right, talks with former U.S. Secretary of State Henry Kissinger, left, at the Great Hall of the People Tuesday, March 17, 2015 in Beijing, China. (AP Photo/Feng Li, Pool)

President Barack Obama, Chinese President Xi Jinping, first lady Michelle Obama and Chinese first lady Madame Peng Liyuan wave from the Truman Balcony of the White House in Washington, Friday, Sept. 25, 2015, after a state arrival ceremony for the Chinese president on the South Lawn. (AP Photo/Evan Vucci)

U.S. Secretary of State John Kerry, left, jokes about his height with former NBA basketball player Yao Ming during the U.S.- China High Level Consultation on People to People Exchange at the National Museum in Beijing, China, June 7, 2016. (Saul Loeb, Pool Photo via AP)S

FILE - In this Feb. 15, 2012 file photo, Chinese then-Vice President Xi Jinping and Iowa Gov. Terry Branstad, right, raise their glasses during a toast at a formal dinner in the rotunda at the Iowa Statehouse in Des Moines, Iowa. The 70-year-old Branstad was confirmed Monday, May 22, 2017, as the U.S. ambassador to China. Branstad has no formal diplomatic experience, though his relationship with Chinese President Xi Jinping dates to the 1980s, when both men were in early stages of their careers. (AP Photo/Charlie Neibergall, File)