NEW YORK The relationship between the United States and China is beset by ambiguity. On the one hand, seven presidents have affirmed the importance of cooperative relations with China and a commitment to a one-China policy. Nevertheless, ambivalence has suddenly re-emerged. Various U.S. officials, members of Congress and the news media are attacking China's policies, from the exchange rate to military buildup, much of it in a tone implying that China is on some sort of probation. Before continuing on this subject, I must point out that the consulting company I chair advises clients with business interests around...