When Americans assess the relationship with Pakistan, one of the motivators for continued engagement is the idea that if the US withdraws, the PRC will step in and that such a development would be bad for US interests in the region. This line of thinking has always stuck MILINT as naive. The PRC has a long established relationship with Pakistan that remains close irrespective of what the US does. Pakistan has enjoyed that unique position of being in the middle of two great powers - a position ripe for manipulation and profit. It has generally played that hand quite deftly. Yet as normality continues to lose its grip in Pakistan, the potential for increased tensions with China exist.
America is having a hard time convincing Pakistan to get its house in order for a variety of reasons: distance (physical, political, cultural), economic crisis at home, comparatively small military footprint WRT Pakistani territory, questionable will to seriously confront Pakistan and so on. China does not have any of those problems. If China assesses that the Islamist threat in its west is getting out of control and emanates from sanctuary in Pakistan, its old ally better look out. The Chinese wont care if its reaction (read: use of force) offends anyone in or outside of Pakistan, it wont be limited to individually targeted strikes against specific high value targets, and it wont stop, for financial, political or moral reasons until the job is done. This is yet another area where US and Chinese interests are coalescing. The question is will Washington grasp the opportunity and use it creatively?