A prominent American economist has cautioned that the United States and China risk developing a “fixation” with national security, a tendency he said was distracting from the domestic challenges facing both countries.“We’ve taken the concept of national security too far,” said Stephen Roach, a senior fellow at Yale Law School’s Paul Tsai China Centre, at the US-China Hong Kong Forum on Monday.He called on Washington and Beijing to draw a clear distinction between economic and national...