Social security is self funded and is actually a buyer of US debt. So there is no direct connection between social security shortfalls and US gross federal debt.

To be slightly fair to the parent comment, it seems at least a bit valid to choose whether to consider the social security tax to be revenue to the government and social security payments an expense or to treat them as an entirely separate account. And the social security tax structure at least appears to be quite regressive.

As an analogy: do you think that Costco generates most of its profits from sales of goods or from membership fees? Both answers seem valid.