With all due respect to Jack Balkin, who is a fine scholar, the new claim that the debt ceiling might be unconstitutional under Section IV of the 14th Amendment ("The validity of the public debt of the United States, authorized by law, including debts incurred for payment of pensions and bounties for services in suppressing insurrection or rebellion, shall not be questioned.") strikes me as akin to the right-wing's novel commerce clause claim against the individual mandate. That is, the debt ceiling, like the individual mandate, was seen as incontestably constitutional right up until the moment that it became politically expedient for it not to be. At which point, suddenly, controversy! Forgive me for being skeptical of the development.
Now, maybe the debt ceiling is different because -- until now -- nobody had been dumb enough to make a credible threat to actually follow through on defaulting the American economy. So it never came up until now. Desperate times call for desperate measures and all that. Still, I'm very dubious.