The SSTF is included in our national debt. The "surplus" contributions were invested in T-bills. The USG is obligated to honor those T-bills in much the same way that it must honor the payment of the Chinese T-bills or those accumulated by the Fed.
The most important thing to remember is that even if those T-bills were exchanged for cash and deposited in a CD, SS will still go broke. It is unsustainable actuarily. In 1950 we had 16 workers for every retiree, now it is about three and in 20 years it will be 2 workers for every retiree.
Medicare is in even worse shape. It's trust funds will be exhausted in 2023. And the SS disability fund will be exhausted in 2016. Within the next few years, Congress must approve moving T-bills from the SSTF to the SSDI trust fund to continue making payments. This will impact the effective date the SSTF runs out T-bills.
Semantics and spin is what we got here. We may never know the truth.
The truth is known. You just have to read the annual Trustee Reports for SS and Medicare. What many people don't understand is that we must borrow money to continue to redeem the T-bills in the trust funds so we can pay full benefits.
Also, many do not know that by law, the premiums for Medicare Parts B and D (SMI Trust Fund) cover only 25% of the costs. The remaining 75% comes from the General Fund. In 2012 that amounted to $214.8 billion. In 2012 the GF also had to come up with $97.7 billion to redeem SSTF T-bills. With 10,000 baby boomers retiring every day for the next 20 years, Medicare and SS will eventually consume the entire federal budget if they are not reformed.
These programs are unsustainable because they pay out more in benefits than they collect in revenue. It has nothing to do with the USG "stealing" the money.