And you could ask why the democrats killed it too but I doubt you will.
It is not clear to me that the Democrats have killed the bill. It may be that they are just playing for more concessions from the Republicrats before they pass it.
The only thing I need to ask is why Obama twisted democrat arms to pass TPA if, as the author claims, it limits his power to rule by fiat. His support for TPA and the authors claim that it limits presidential power are totally incongruous and can not be explained by anybody to my satisfaction.