It prevents the taking on of NEW debt if doing so pushes us over the limit.
The President simply will not be able to issue NEW debt to pay OLD debt. He'll just actually have to pay the old debt outright.
This will of course, decrease the money available for his pet social programs, or anything else in government for that matter. He and the other commies in government in both parties, know full well that if this happens, then anything absolutely non-essential - meaning general government and a shadow version of the defense department are on the chopping block if there is not enough cash flow to do it all.