It was Bush who closed our borders, and it was the cry of national security HE rallied that tried to make Canada look like a threat. No matter how you hash it, that is the most damaging thing, and here's why:

When our people can intermingle easily, and actually see each other, and visit and form bonds, no matter what our national leaderships says, we can discover the truth for ourselves. And when you make it hard to do that, and treat people like shit crossing the border (this directed at my own damned government), you're taking away the SINGLE best resource for abusing misconceptions.