House speaker Boehner and a faction of House Republicans are now unambiguously violating the letter and spirit of Section 4 of the 14th Amendment.

FORTUNE — As we enter the final countdown in our third debt-ceiling crisis in two-and-a-half years, most of us have heard at least some discussion of Section 4 of the 14th Amendment, which dictates that the “validity of the public debt of the United States … shall not be questioned.”

Unfortunately — and misleadingly — these mentions have often occurred in the same breath as the notion of minting two $1 trillion platinum coins as a way of magically and comically circumventing the impasse. This has led many to assume that the 14th Amendment’s relevance to the crisis is as hypothetical and far-fetched as the wacky coin proposal, amounting to no more than some sort of “silver-bullet” pipe-dream or a liberal academic’s Hail Mary pass.

That is wrong. It is true that the majority view, both in legal academia and among President Obama’s legal advisors, seems to be that the 14th Amendment provides no easy out for the President as he faces this crisis. It does not, in their estimation, authorize him simply to declare the debt-ceiling a nullity and order the Treasury Department to issue new debt without prior authorization from Congress.

Still, the fact that Section 4 of the 14th Amendment may provide no deus ex machina from our current predicament, as Harvard Law School’s Laurence Tribe put it in a New York Times op-ed piece in July 2011, does not detract from the fact that the provision exists, retains vitality, speaks directly to our situation, and ought to weigh very heavily in the minds — and on the consciences — of the House Republican faction that is now unambiguously violating its letter and spirit. The very same eminent constitutional scholars who have publicly counseled Obama not to nullify the debt-ceiling law itself in reliance on Section 4, including Tribe and Jack Balkin of Yale Law School, have nevertheless acknowledged that the Framers of that provision did, indeed, mean to bar Congressmen from using the threat of debt-default as a coercive tool in the arsenal of everyday politics. They simply doubt that the provision empowers President Obama to start issuing debt without Congressional authorization, which would violate other Constitutional provisions. (At least two other eminent scholars, on the other hand, Neil Buchanan of George Washington University Law School and Michael C. Dorf of Cornell Law School, do believe President Obama has that so-called “nuclear” option, for reasons they laid out in this Columbia Law Review article in October 2012.)

MORE: Buffett likens debt fight to ‘nuclear bombs’

Though triggered by specific threats the country faced in the aftermath of the Civil War, Section 4 of the 14th Amendment remains relevant to our world. Yale’s Balkin explained on his Balkinization blog in June 2011: “Section 4 targets the worry that, once fully readmitted to the Union, senators and representatives from Southern states … would deliberately refuse to repay debts incurred in suppressing the confederate rebellion.” Still, he continued, the provision “was stated in broad terms in order to prevent future majorities in Congress from repudiating the federal debt to gain political advantage, to seek political revenge, or to try to disavow previous financial obligations because of changed policy priorities.”

At the time of the provision’s drafting, in fact (again, according to Balkin), Senator Benjamin Wade, the leader of the Radical Republicans and the driving force behind the section’s enactment, explained that by widely guaranteeing the security of federal debt, the provision “will give great confidence to capitalists and will be of incalculable pecuniary benefit to the United States, for I have no doubt that every man who has property in the public funds will feel safer when he sees that the national debt is withdrawn from the power of a Congress to repudiate it and placed under the guardianship of the Constitution than he would feel if it were left at loose ends and subject to the varying majorities which may arise in Congress.”

Why, then, do Balkin and Tribe and others think Obama cannot declare the debt-ceiling invalid? After all, it is Congress itself that has set the spending levels and taxation levels, and those decisions, once made, determine the level of debt that is required to avoid default as a matter of simple arithmetic. The shortfall between tax revenue and spending is obviously the amount that must be borrowed, so hasn’t Congress, in effect, already authorized this level of borrowing? Having a law that sets a ceiling on borrowing to cover spending Congress has already authorized seems both superfluous and an invitation to default. For this reason Henry J. Aaron, a senior fellow at the Brookings Institution, recently described the ceiling in the New York Times as “the fiscal equivalent of the human appendix — a law with no discoverable purpose.”

Worse still, the debt-ceiling law (dating in its current form to 1939) seems to bake in crisis by promising to place the President in potentially impossible binds every time the ceiling is reached. (And even if we reduce our deficits, we will still keep bumping up against it, Buchanan and Dorf observe, because it is defined as a flat sum of dollars rather than as a percentage of national income.)

MORE: Nina Easton: Dazed GOP leaders search for exit sign

The inevitable crisis arises because the President has a Constitutional obligation to “take care that the laws … be faithfully executed,” which means spending money at the levels Congress has mandated. Yet his only source of funds with which to do so are the revenues Congress permits him to raise via taxes or the funds it permits him to borrow by issuing public debt. (The Constitution gives Congress control over all three functions: spending, taxation, and borrowing.) If the President fails to come up with the requisite money to spend, he’ll default on the public debt in violation of Section 4 of the 14th Amendment.

So the debt-ceiling law places the President in what Buchanan and Dorf call a “trilemma,” with no way out. Under the Constitution, he can’t default, he can’t unilaterally raise taxes, and he can’t unilaterally borrow. In such a predicament, those scholars believe he is obliged to take the “least unconstitutional” approach, which, for reasons they outline, they think would be invalidating the debt-ceiling and issuing new debt — which they call “Presidential debt,” because it would have no Congressional authorization.

Tribe and Balkin disagree. They think the President would be relegated instead to some sort of “prioritization” process, where he directs those limited funds available to him to making certain that the country honors its outstanding bond obligations — the most unambiguous focus, they contend, of Section 4 of the 14th Amendment — and to funding other absolutely essential functions while allowing most other obligations (salaries, entitlements, contracts, etc.) temporarily to go by the wayside, though this would obviously cause enormous pain and upheaval throughout the country.

To be sure, there are also practical considerations that appear to underlie and color scholars’ competing interpretations of the constitutional text and history. Some think that “Presidential bonds,” for instance — those issued without Congressional authorization — would not find a market, rendering them an unworkable solution in practice. Others, like Buchanan and Dorf, think “prioritization” is impossible as an administrative matter because of the vast number of payments involved and the way the Treasury’s payment systems are currently wired.

MORE: Four debt ceiling scenarios freaking out traders 

But the bigger point is this: Section 4 of the 14th Amendment exists, and it is all about trying to ban precisely what’s going on right now. The only question is how it applies. And even that uncertainty tells us something very important about the gravity of the crisis we are facing today. The reason we have so few precedents to guide us in applying Section 4 is that, by and large, the provision comes into play only when a critical mass of members of Congress are willing to see grievous harm come to our nation if their demands aren’t met — demands that cannot be achieved through ordinary democratic processes. That’s a situation that we really haven’t faced since Civil War Reconstruction, when formerly hostile, armed insurgents were being reintegrated into the Union and, therefore, into Congress.

The President is not the only one who has sworn an oath to uphold the Constitution. Members of Congress, too, have an obligation to support and defend it — including Section 4. The House members currently using the prospect of debt-default as a bargaining chip — whether to delay implementation of the Affordable Care Act or to achieve any other goal — are betraying the Constitution, and the President is correct to draw a line in the sand and refuse to legitimize this abuse or incentivize its recurrence. He deserves immediate, full-throated, bipartisan support for putting an end to this constitutionally forbidden tactic once and for all.