People do not change. Human nature is the same now as it was in 1861, or 1775 or the day that that Cain slew Abel, for that matter. Faced with the imminent loss of power (and probably the means of food and energy production) the Federal government will put boots on the ground in your hometown faster than you can say "Abraham Lincoln". And all it takes to force a soldier to obey any order is put another soldier behind him with orders to shoot him if he hesitates. It worked for the Soviets, and it would work for Barack.
Ah, but culture does change.
Witness the tectonic shifts in our culture over just the last half century. We lost a winnable war in South East Asia at the end of the sixties because the pressure of cultural changes in attitude toward war forced us to abandon that cause.
Institutionalized racial discrimination (at least against minorities) is now a thing of the past because of attitude shifts in the culture.
A rebirth of national pride and patriotism has burst upon the scene after decades of decline. That rebirth was of course preceded by events that snapped most of the culture out of its collective apathy, but the fact is, it's here and it's growing. The very fact that we're even having this conversation, or the fact that this website even exists, are testaments to that monumental shift in the culture.
My point is, what was a predictable response to events in one age, is not so predictable in another. The western powers once went to war because of the assassination of a head of state. That war killed millions of people. That wouldn't happen today. Neither will a military response to an issue of secession.