While throughout the Cold War, the US did have nuclear war plans for hitting China alongside the Soviet Union, starting the 1960s they also started drafting and implementing war-plans which involved ignoring the Chinese and focusing exclusively on the WARPAC. I believe the first of these was a variant of the SIOP implemented in 1961 which included a "hold" option against China.
Whether the US nukes China or not is really dependent on what China does during any crisis/conventional conflict in the run-up to the nukes flying and how the US interprets those actions.
Of course, I should have qualified that I was thinking in terms of an "everything must go" Major Attack Option scenario that the thread seems to invoking