Why do they say Social Security checks are in danger if the debt ceiling limit isn't raised, yet there is supposedly a trust fund for it?

I know the obvious answer is “the money is all coming from the same pot.” But why has this distinction been made in the past, but at the moment it isn’t? Is it just pure politics to instill fear?

This trust fund is supposedly $2 trillion, and only to be used when the So. Sec. revenue no longer can keep up with the payouts. The forecast is it will be needed in 2017, and should be depleted between 2037 and 2053. At that point only 70% of promised payouts will occur without help from the Treasury.