The Canadians say the Clinton campaign has also told them that her abysmal campaign rhetoric should not be taken too literally. One hopes that is the case. This leads Noam to add, tongue in cheek (I hope):
What is it with these Canadians? Are they running some sort of entrapment operation up there? Why do they keep trying to torpedo Democratic candidates?
But why shouldn't the Canadians respond to threats made against them? NAFTA isn't all about the USA after all, Canada and Mexico have interests too.
Or, to put it this way, imagine if a British would-be Prime Minister ran on a platform that called for opting out of NATO. Don't you think the Americans might point out that this was a bad idea and one that would have consequences for all areas of the US-UK relationship? I rather suspect they would, don't you?
And of course the Americans aren't always known for their restraint when it comes to interfering in other people's elections. At a (very) minor level, recall Ronald Reagan's refusal to meet poor old Neil Kinnock, leaving him to kick his heels in a White House ante-room. Mrs Thatcher was going to win the 1987 election anyway, but Kinnock's humiliation dealt a pretty severe blow to his pretences to statesmanship.
UPDATE: Dan Drezner gives you his indispensable Rules to Understanding Canadian-American Relations.