He has access to more intelligence then you and I. He must legitimately feel Canada is a threat to our security. Possibly even imminent invasion, or hostile action. He has the intelligence.
Someone who will persist in a racist lie of birtherism conspiracy nonsense for five years, has zero credibility. What this person "legitimately feels" is so totally out of scope because first his assertions of fact are frequently provably not reality based, second there is no ability to assess anyone's feelings. Why must he legitimately feel Canada is a threat? Why can't he be lying about it just to get what he wants, whatever that is?
> Harold: "Red! We found an old bomb in the lake! What do we do?!"
> Red: "Call the American Air Force."
> Harold: "We tried, but it's in the Canadian side of the lake, they can't help!"
> Red: "Then call the Canadian Air Force!"
> Harold: "It's after 5, he's gone home."