The US fought a war of attrition for 20 years and finally withdrew, their enemy being in a better position than before the invasion. You wouldn't call that a defeat?
Why exactly do you think that a better armed and much larger force, one that is the economic backing of the military they'd be facing, would stand less of a chance?
I'm not saying it is going to happen, I'm only saying it can happen with an armed population, and cannot happen without an rmed population.
"Political will" is something that happens in populations, not a leadership class. The US chose to end a war of attrition because they lost. Plain and simple.
In the event of some domestic problem going that far there would be basically no political will to continue military action, and if the government continued without that it would quickly be viewed as illegitimate, lead to instability and a larger uprising.