Trade is one of the stranger political issues in recent years. For more than two decades now the left has been saying that the trade deals (even going back before the Uruguay Round of GATT negotiations), are not really "free-trade" deals at all, but are rather 'corporate rights' deals that are intended to strengthen the power of multinational corporations to set the economic agenda at national and international levels. There has always been plenty of evidence for this and the recent kerfuffle over CETA has demonstrated this remarkably well. These deals almost all contain clauses that strengthen the ability for foreign or multinational organizations to determine domestic economic and even social policy.
The main political parties in many Western nations have overwhelmingly supported these deals and done a great deal to hide the fact that these deals are not really concerned with open trade per se, but with the suppression of national governments' ability to institute policies that will protect their populations from outside forces. The Democrats and the Republicans in the US, for example, have always, with few exceptions, promoted these deals. Thus it comes as some surprise that a guy like Trump, who as far as I can tell never spoke against these deals until the past year or so (and has certainly taken advantage of these deals to increase his own wealth), is suddenly telling people that NAFTA and other such "trade deals" have been bad. (It is not, of course surprising that Bernie Sanders has spoken against such deals; he has been consistent on this issue throughout his career) It is predictable that much of the Republican establishment is upset by Trump's critique in this regard, given that the Republicans (even more than the Democrats) have promoted and benefited from these deals.
What is a little bit surprising is to see some Republican operatives (people who have supported so-called free trade for years or even decades) try to criticize Hillary Clinton for being in favour of them. Many Republicans have tried to use leaked speeches given by Clinton in which she talks of "open borders" as a strike against her, even though what she has actually said matches exactly what the Republicans have always said. The problem is, of course, that the phrase "open borders," a phrase that used to be associated specifically with the freer movement of goods and services, has now become associated with the movement of people. This is because of the way the rightwing in the US has been talking about the issue of undocumented workers and the perception among many Republicans that Democrats just want to fling open the borders with Mexico and let everyone stream across into the US. (Whether any Republicans actually believe that any Democrats sincerely want this, is somewhat irrelevant. What is important is that they have used the idea as a political tool) But when Ms. Clinton used the phrase "open borders" there is no reason to believe that she meant the free movement of people (in economic theory terms we can read the word "labour" here). Because with the exception of the European Union, no modern trade deal has ever included the free movement of people as individuals who are trading the commodity of their own labour power. The kinds of deals that Clinton and the Republicans have supported for decades are never concerned with the most common and most traded commodity in the world: labour power.
Thus when Trump's various surrogates (particularly men like Newt Gingrich and Rudi Giuliani) criticize Clinton for 'secretly' wanting to open the borders to anyone in North and South American who wants to come the the US and work, they are knowingly misleading people, and being supremely hypocritical. They are fully aware that Clinton's agenda is the expansion of already existing "free-trade" deals that are concerned with a) reducing trade barriers, and b) (and more importantly) giving corporations and other nations the ability to suppress social and economic programs in other countries. But even if Clinton were talking about a North/South American Union similar to the EU, where people were allowed to cross borders to work in different countries (and there is absolutely no reason to believe that she has ever promoted this), this would, in fact, be the logical outcome of any real notion of actual 'free-trade,' since to exclude the free movement of labour from a trade deal actually means to exclude the most important and commonly traded of all commodities.
Either way, if you look carefully, you can see Donald Trump's pant on fire.