Trade talks between the U.S. and China are in danger of hitting an impasse, threatening to derail the Trump administration’s plan for a limited “phase-one” pact this year, according to former administration officials and others following the talks. Both sides remain divided over core issues—including Beijing’s demand for removing tariffs and the U.S.’s insistence on China buying farm products—nearly six weeks after an “agreement in principle” was announced by the White House on Oct. 11. …