Identify a reason why Social Security as it currently exists is unsustainable in the long run. The overall U.S. population is shrinking because of decreasing life expectancy. so soon there would not be enough taxpayers to fund A the Social Security program. B. Income tax revenues that form the largest source of funds for Social Security programs are projected to decline in the long run. OC. Individual income that is subject to Social Security taxes is capped at about $117,000 D. Corporate income that is subject to Social Security taxes is capped at $1 million