Whether we like it or not, welfare, unemployment and medicaid are more geared towards national security than humanitarian efforts. I doubt that 20% of the people could win a war but I don't think that citizens will be quick to choose a side and a lot of deaths will result from non-participation.
It's fun to think of defending a location until back-up arrives. In Hopewell a city of 25,000 there are only 60 police officers, 20 or 30 sheriffs but the older residents are 25% of the pop. Most American cities are similar in make-up.
Due to the Patriot Act, the government knows who owns weapons and has a way of contacting those citizens; email addresses, ip adresses, cellular and the ability to send messages directly to certain television sets. Hence the reason for switching to digital versus analog.
Victory will never happen, people that earn below $20,000/yr have no allegiance to big business, the government or comfort and they are breeders of the criminal echelon but are rarely participants. The falling middle class will attack them first. Most of their men are incarcerated, the boys will shoot but their marksmanship is far from adequate.