In short, when things get that bad, order that would instill and uphold that value has already broken down and oaths don't mean so much. It becomes about choosing sides, interests and loyalties, etc.
In theory, a president could come out of left field with blatantly dictatorial actions (and we'd smack them down), but in a strong democracy like ours or Canada's, for something like that to have a chance of working, it would require significant erosion of norms and values over quite a period of time, or some kind of crazy natural or economic disaster, or a military invasion.