The US has a very fragile internal logistics structure. Just in time stocking means that you can run out very quickly.
And I don't think that the majority of the military will side with us. They will follow orders, because the alternative is summary imprisonment and execution. Look at all the plots against Hitler in the German army. They hated the guy, but didn't take action because the military culture is one where you follow orders. Not mutiny.
Now, if the fight went long, more and more would cross over. But the likelihood of a long civil war in the US is pretty remote. If, say, Montana tried to secede, most of the infrastructure can be wiped out in less than a day by the Air Force.
We need to stop hoping for a civil war or revolution. Besides the millions of deaths, remember that very few such actions have succeeded without the support of another power.
And a bunch of other states would immediately secede.