Charlie asks, "Is the debt ceiling constitutional?"
I'll answer with another question: Imagine congress doesn't resolve the debt ceiling crisis, we are being forced to default on our debts. Everyone predicts disaster. Markets are maybe starting to panic. Obama says, "You know what? I'm not going to default on the US debt. Turns out I think the debt ceiling is unconstitutional, because the fourteenth amendment guarantees that the federal government's debt can't be questioned." Markets calm down and everything proceeds as normal.
Now my question: Does John Roberts want to keep Obama from doing that, revive the crisis, and go down in history as the man who destroyed the global economy over an arcane constitutional debate?
My answer is "no." I suspect, if it comes to that, he'll avoid the question of constitutionality altogether and say that no one has standing to sue the president (IE, no one can demonstrate a clear harm) and/or invoke the political question doctrine (the idea that, when the law is unclear but clearly leaves an issue to other branches of government, courts should let coequal political branches resolve questions with policy decisions, not make up laws and resolve the question with a legal decision).
If you want to hear all the dumb legal arguments, this is a good summary. But this isn't really a legal question, it's a is-John-Roberts-crazy-or-blind-to-how-history-will-judge-him question. And he answered that when he voted to uphold obamacare.
Charlie's other question is harder, and I'll get to it in time.