TL;DR: Its from the Civil War and the US can’t simply decide that debt it has incurred is invalid
In the clip titled “Biden to Give Up IRS Funding That Fights Rich Tax Evaders In Debt Ceiling Fight”, at timestamp (9:22), John asks when the text of the Fourteenth Amendment could possibly apply, if not with respect to the debt limit. Cenk agrees and reads the text as “The validity of the public debt of the United States, authorized by law, shall not be questioned.”
The actual text of the 14th Amendment is: “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. But neither the United States nor any State shall assume or pay any debt or obligation incurred in aid of insurrection or rebellion against the United States, or any claim for the loss or emancipation of any slave; but all such debts, obligations and claims shall be held illegal and void.”
The situation in which this clearly would apply, is where the US government decided that debt it had incurred was illegitimate, and therefore, would not be paid back. Argentina has taken this position in recent decades, and France took a version of this position following their revolution: the Kingdom of France no longer exists, so don’t expect the Republic of France to pay its debt. (Interestingly enough, the United States also took this position following France’s revolution - as our first president, George Washington, told the French ambassador that the debt the United States incurred to France as a result of the American Revolution was owed to the Kingdom of France, not the Republic of France. And considering that the Monarchy had been decapitated, the United States felt the debt was noncollectable, but I digress…)
The language of this amendment, however, does not apply, where the U.S. government acknowledges its debt as legitimate, but simply decides that it doesn’t want to borrow the money to continue making payments.
The historical context is instructive. At the time the 14th Amendment was passed, both the Federal United States Government and the Confederacy had incurred large sums of debt. Creditors who lent money to the Confederacy were SOL - the Confederacy ceased to exist and the Federal Government of the United States (the “Union”) wasn’t about to pay creditors that “aid[ed ] insurrection or rebellion against the United States.” Nor was the Federal Government of the United States (the “Union”) going to pay slaveholders - the people who would “claim for the loss of emancipation of any slave”. The Union wanted to make it clear that if you lent money to the confederacy, or if you wanted to complain about economic loss due to losing slaves, “all such debts, obligations and claims [were henceforth] illegal and void.”
What impact did this have to the South? Well, they were pissed. Not only did they lose the war, but now their creditors weren’t going to be paid back. And their creditors, (that is, creditors of the Confederacy) were southern landed elites. They were families who were economically powerful, politically important, and well-respected (albeit, from a Southern perspective). So the Southern states now forced back into the Union did so under the protest that if Southern creditors weren’t going to be paid back, neither should Northern, Union creditors, because the war was, after all, a war of Northern aggression and the South was just defending itself (again, from a Southern perspective).
This made the Union’s creditors nervous. If there was a chance that they weren’t going to be paid back, then the risk of lending to the Federal Government of the United States would go up, and interest rates along with it. Hence the language of the first line of the Fourteenth 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.”