To quote the Forbes piece:
To put it another way, the total unfunded indebtedness of Social Security and Medicare comes to $106.4 trillion. That is how much larger the nation's capital stock would have to be today, all of it owned by the Social Security and Medicare trust funds, to generate enough income to pay all the benefits that have been promised over and above future payroll taxes. But the nation's total private net worth is only $51.5 trillion, according to the Federal Reserve. In effect, we have promised the elderly benefits equal to more than twice the nation's total wealth on top of the payroll tax.
Of course, theoretically, benefits could be cut to prevent the necessity of a massive tax increase. But how likely is that? The percentage of the population that benefits from Social Security and Medicare is growing daily as the baby boom generation ages and longevity increases. And the elderly vote in the highest percentage of any age group, so their political influence is even greater than their numbers.