For Trump to say that the US 'has been so badly taken advantage of' makes that country sound like a 12 year child instead of the leading economic power on the planet. Or maybe it's just Trump sounding like a 12 year old child. 

If he truly believes the deal was bad for the US, it wasn't because of Canada or Mexico - it was the agenda of American business. That said, the real failure in the US is the refusal of the American government (and its electorate) to put in place domestic social and economic policies that take into account the realities of the new global economy. 

A similar failure in British politics led to the Brexit vote. US withdrawal from NAFTA, or in Britain's case the EU, will harm the withdrawing party as much as anyone else. It would be nice to think that the voters in both countries will soon recognize the bill of goods they've been sold by conservative economic orthodoxy in both cases.