The US can always pay its debt because it is denominated in US dollars - it can print sufficient US dollars to meet its debt obligations. States do not have this ability.
It might be if it had a constitutional amendment saying Medicaid, Medicare and/or Social Security were untouchable. It doesn't. There's no spending in the US that's not on the table. When or if push came to shove it's not hard to imagine some or all of those programs being cut just as it's not hard to imagine taxes going up.