Complex sentence: If the debt ceiling is not raised, then the Treasury prioritizes the items to pay with its ongoing revenue stream and it could choose to pay interest on the debt so the U.S. does not default on the sovereign debt.
Split into simpler sentences: If the debt ceiling is not raised, then the Treasury will prioritize the items to pay with its ongoing revenue stream. Treasury could choose to pay interest so that the U.S. does not default on its sovereign debt.