The White House is impatient for Chinese President Hu Jintao’s Jan. 19 state visit, but not to talk about China. Instead, the critical agenda item is North Korea. Deputy Secretary of State James Steinberg recently led a delegation to Beijing seeking help in persuading Pyongyang to cease its provocations. Publicly, Beijing has stood by its neighbor through it all, from the sinking of the South Korean warship Cheonan in May to the lethal shelling of Yeonpyeong Island in November. Privately, though, U.S. officials are convinced, China’s support is wearing thin.