About the debt limit - could someone explain this to me?

There's this...

14th Amendment
Section 4. 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....

http://en.wikipedia.org/...

...and this...

At the start of each new U.S. Congress, in January of every odd-numbered year, newly elected or re-elected Members of Congress – the entire House of Representatives and one-third of the Senate – must recite an oath:

    I do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter.

http://en.wikipedia.org/...

...and this!

The oath of office of the President of the United States is an oath or affirmation required by the United States Constitution before the President begins the execution of the office. The wording is specified in Article Two, Section One, Clause Eight:

    Before he enter on the Execution of his Office, he shall take the following Oath or Affirmation:—“I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the United States.”

http://en.wikipedia.org/...

Would someone please explain to me just how the debt limit law is legal in the first place?  If it is constitutional, just how could congressmen refuse to raise the debt limit without violating their oaths of office?

And if congress violates the Constitution by refusing to raise the debt limit, doesn't the president's oath of office require him to raise it unilaterally?

Seriously, what's up with this?