when under bush jr, sino-america relation was at the best time, maybe never would be at that level again. america needed china that time, even allowing china's military guys going to gitmo to question uighurs!

now obama basically got out of islamic mess, and the tradition of bad relation when under democratic party also holds.

that's why you see it now, xi indeed is more aggressive, but major reason is still america. the best example is its role in sabotaging sino-japan relation.