Jack the list is very long and wide.  Beyond just impacting the two economie trade intigration here are a few others.  Geopolitics. Canada and Mexico go from countries with vested interest in the USA to ambivalent neighbor's.  It matters, we for example will do deal with your competitors and they will then be vested in Canada.  Take China, lets say they are tapping into our oil and depend on it.  Think they will roll over if a ME war happens and the USA demand access to our oil.  The agreement ends and the USA and it bully cankiss my. ....  There is the whole shaking a hand with a unreliable partner, think the world isn't watchinh the USA.  Well maybe America thinks it can go it alone with it pop maybe not.  Keep in mind China is driving the world economy, look at Australia...booming!  China will soon have the largest economy in the world.  Keep in mind that there are lines of country that hate the USA, that would love to see it isolted even from its neighbors. This is just scratching