By all accounts, it looks like a deal is about to be announced in which the debt ceiling is hiked in exchange for the promise of major spending cuts, including to entitlements, totalling at least $2.4 trillion.

Anything can happen, but it apppears the GOP is on the verge of pulling off a political victory that may be unprecedented in American history. Republicans may succeed in using the threat of a potential outcome that they themselves acknowledged would lead to national catastrophe as leverage to extract enormous concessions from Democrats, without giving up anything of any significance in return.

Not only that, but Republicans — in perhaps the most remarkable example of political up-is-downism in recent memory — cast their willingness to dangle the threat of national crisis as a brave and heroic effort they’d undertaken on behalf of the national interest. Only the threat of national crisis could force the immediate spending cuts supposedly necessary to prevent a far more epic crisis later.

Under the emerging deal, President Obama can hike the debt limit in two stages — the first in exchange for equivalent cuts; the second after a Congressional committee comes up with second round of yet more cuts, including to entitlements. The talks appear close to resolving the spending cut“trigger” that would force the committee to act — without giving the GOP an incentive to deliberately sabotage its work. The remaining question is how to get it through the House. But a deal seems immiment.

Again and again, Dems drew lines in the sand that they promptly erased as the threat of default grew. A clean debt ceiling hike? Dropped. Cuts to Medicare benefits? They’ll likely be in that committee’s crosshairs. The insistence on revenue hikes? Withdrawn.

What make this all the more remarkable is that throughout this process, Republicans themselves conceded not just that a debt ceiling hike would be disastrous for America, but also that it was inevitable. Yet they were still able use the threat of default as leverage. How?

The simple answer: Dems weren’t prepared to allow default — no matter what. Republicans, by contrast, treated the debt ceiling hike as a necessity, but one that had to happen on their terms. In a remarkable act of political cynicism, they recast the debt ceiling hike itself as a GOP concession — even though they had already agreed it had to happen to avert an epic national crisis. And Dems made this possible by accepting the dynamics of the situation as Republicans defined it. Whether there was another alternative for Dems is another question.

If Dems had refused to budge from the demand for a clean hike, would Republicans have blinked — or would they have allowed default? The bottom line is Dems weren’t prepared to take that risk, and the fast-approaching deadling meant moving to negotiations was imperative. Should Obama have waged a far more aggressive P.R. campaign to saddle the GOP with potential blame for default? Maybe, but public opinion in recent days was running strongly for compromise and against Republicans — and they still continued to use the threat of default as leverage. Could Dems have had more success with a more aggressive approach? We’ll never know. Call it the road not taken.

The road that was taken is leading to a deal in which Dems are aggreeing to take huge amounts of money out of the economy when the recovery is shaky at best. It also seems to ensure that Dems will agree to entitlements cuts heading into an election where the GOP was supposed to be deeply vulnerable over their drive to end Medicare as we know it. Dems will promise to salvage victory in the form of “smart” entitlement reform. Maybe so. For now, it appears the GOP is on the verge of a huge and unprecedented victory.

UPDATE: As Jonathan Cohn notes, maybe the deal won’t be quite as bad as it seems, but this is the last chance to make as much noise as possible.