That's a straight-up lie. Buchanan is against imperialism. Hell, he wrote a book titled "A Republic, not an Empire" (very good by the way).
Buchanan is not crazy at all. Usually, people just make things up about him out of thin air, because the truth is that Buchanan is a smart, knowledgeable guy.
If you are claiming the Canadian Annexation is a lie, here is something I pulled down from the web:
Quebec: Offer seceding provinces alliances or statehood
Canada has not been a security concern in this century. That is changing. Quebec may declare independence, and the Maritime and Western provinces could separate from Ottawa. Americans may profoundly regret a breakup of Canada, but we are not a disinterested party; Canada is the most important country on earth for us. Should it come apart, the US should offer trade agreements and security alliances to each successor state, and statehood itself, should any breakaway Canadian province wish it.
Source: “A Republic, Not an Empire,” p.370
His colume was much more aggressive.
Can you not read?
He said that if Canada breaks up, we should promote stability amongst the remnants- including offering statehood.
He did not say "invade." He did not even say he WANTS that to happen.
It reveals the weakness of your argument when you have to lie about the other guy's.
