Isn't Social Security supposed to be completely funded?

I just have a simple question.

One of the things Geithner has done during the past couple of weeks while mentioning “coffers” is to insinuate that the United States Government can’t be “guaranteed” to have enough money to fund next month’s issuance of Social Security checks.

Does that money really exist there?  If not, where did that money go?

If Geithner and Obama’s threat not to pay the benefits is to be taken seriously, the first question everyone should be asking is:  “What happened to all that money?  I thought it would be there no matter what?”  Unless I’m reading these two guys wrong, they’re saying it just doesn’t even exist!