The validity of the public debt of the U.S.....shall not be questioned (14th Amendment)

[Yo_Mama]

15. I think you are quite wrong

Under Section 8 of the Constitution:
http://www.law.cornell.edu/constitution/articlei#section8
"To borrow money on the credit of the United States" is one of the Congressional powers.

Only Congress has the power to borrow money, but it does so by means of the Treasury (Dept of Treasury executes the borrowing Congress has authorized).

Once the money has been borrowed, of course the "full faith and credit" clause comes in - but note Congress has disregarded it before when defaulting on the Liberty bonds.

Because it is Congress which has instituted the debt limit, borrowing money over the current debt limit is by definition outside the power of the Treasury Department. It is true that authorized spending may allow branches of the Executive to go to the Treasury for money raised by issuing debt, but the Treasury does not have the legal authority to raise the authorized debt limit.

Congress can appropriate revenues and spending, but when revenues fall short that doesn't mean that the Executive can borrow, given that Congress has explicitly set a limit (albeit often changing) on the debt limit. Congress doesn't have to set a debt limit, but it certainly has the constitutional power to do so, and when it has done so, no other branch of government has the right to ignore that debt limit.

By definition, if Treasury were to issue debt over the current debt limit it would be a debt NOT "authorized by law", which is what the 14th Amendment covers:
http://www.law.cornell.edu/constitution/amendmentxiv

In any case, as a practical matter, if Treasury were to issue bonds that had the effect of exceeding the legal debt limit, it is likely only the Fed would buy them, because it is probable that at a later date they would be first in line for default due to never having been legally authorized and therefore not subject to the 14th Amendment.