So as we go tit for tat with China, we can obviously put more tariffs on them because we import more.  

But suppose when China runs out of US stuff to put tariffs on they decide to forego buying US Treasuries at our next auction, opting for Europe or some other vehicle to put their hoards of cash?  Or worse they opt to dump some US Treasuries.

My expectation for Trump, if he has the power, is that he says to China, "Screw you. We are only going to pay 50 cents on the dollar for what we owe you."  (Kind of the way he has conducted himself for 30 years in the private sector.)   Even just the threat of it would cause a panic world wide I would think.  

Question:  Does he have the power to make such a move?