This essay from the Strategic Studies Institute notes that it is precisely our home morale that places our long war at risk and not the capabilities of any of our enemies:
The costs associated with these small wars and interventions transcend straightforward accounting. Their human, physical, fiscal, political, psychological, and even moral demands challenge what is proving to be a very vulnerable grand strategic center of gravity for the United States—the population and its willingness to accept the high price of great power. Indeed, political elites and opinion leaders must either inure the body politic to the costs associated with exercising great power or face the consequences of diminished U.S. influence.
And retreat would create a whole host of problems. So before people lightly call for sacrifice, consider how long we must fight this war and how much we must do globally to keep the world in a condition that allows our freedom and prosperity to flourish. We have the power to keep going. We don't need sacrifice to generate power. But excessive sacrifice can erode our morale and chisel away at our weak point.