"Nothing stops this train" is Lyn Alden's shorthand for the same constraint "The Debt Constraint" laid out: once a government's interest payments grow large enough relative to revenue, raising rates to fight inflation increases the deficit faster than it slows demand, and monetizing the debt becomes the path of least resistance. If you haven't read that piece, that's enough of the mechanism to follow this one — it's self-reinforcing, and it binds well before it becomes a visible crisis.
Alden's contribution isn't a new mechanism. It's an argument about why the constraint doesn't get resolved once it exists. In her own accounting, the drivers behind persistently large deficits are structural rather than incidental — entitlement spending tied to demographics that don't reverse on a useful timeline, healthcare costs that resist most cost-control policy, defense spending protected by its own political coalition, and a level of polarization that makes touching any of the above harder than usual. Four separate political blockers, active at once, is a different situation than one temporary obstacle to work around. It's not that spending cuts or tax increases are impossible in principle. It's that every plausible path to them is blocked simultaneously — which is what makes monetization look less like the worst option and more like the only one nobody actually has to vote for.
For someone planning a retirement that spans forty years, this matters more than the current inflation rate or the current safe withdrawal rate guidance. A 3.9% withdrawal rate—Morningstar's current figure for 2026—reflects elevated equity valuations and bond yields that are elevated but not generous. Morningstar bases its guidance on historical simulation—looking at past returns and past inflation to determine what withdrawal rate would have survived. But it can't simulate a fiscal mechanism that hasn't yet played out at this scale in the United States. It assumes the historical relationship between returns and inflation holds.
That assumption has two layers. The first is that the currency holds stable in purchasing power relative to a broad basket of goods and services. But there's a second assumption hidden inside that one: that the inflation measured by CPI is the inflation you experience. If healthcare, housing, and food—the largest spending categories for many retirees—inflate faster than the headline number, then your real purchasing power declines faster than the backtest suggests, even if the currency doesn't fully debase.
You can plan for inflation and still miss the problem. A portfolio with inflation-protected bonds, commodities, or real assets can hedge against measured CPI. What it cannot hedge against is the gap between measured inflation and lived inflation—the difference between the basket the government adjusts and the basket you spend from. If healthcare, housing, and food inflate faster than the headline number, and if those costs make up a disproportionate share of your retirement budget, then "real return" becomes a term of art rather than a description of what your money can do.
The natural objection is that this has always been true—inflation has always been a risk, and FIRE planning has always accounted for it. That's fair. The difference now is the size of the fiscal hole and the limited set of tools available to address it without making it worse. The fiscal trap itself isn't new—every government that monetizes large deficits eventually faces currency debasement. What's new is the scale: U.S. debt service is now large enough that rate hikes increase the deficit rather than shrink it, which means there's no normal policy tool available to stop the mechanism once it starts. When debt service is small relative to revenue, a central bank can fight inflation with rate hikes without creating a fiscal crisis. When debt service is large, rate hikes become self-defeating. That's the loop Alden is pointing to.
There's no single number that resolves this. You can't stress-test your way to a withdrawal rate that "solves for debasement" because the mechanism isn't a known rate—it's a range of possible outcomes that depends on political choices that haven't been made yet. What you can do is recognize that a plan built entirely on historical equity and bond returns is a plan built on currency stability you may not have. This means your 3.9% withdrawal rate assumes the dollar's purchasing power stays within historical bands. If debasement accelerates, that rate is no longer safe—not because the portfolio returns worse, but because the denominator is softer. The insurance against that isn't a different withdrawal rate; it's a major spending category that can flex without collapsing your retirement.
If healthcare, housing, and food inflate faster than headline CPI, and you can't cut them, your safe withdrawal rate effectively decreases over time—not because your portfolio underperformed, but because the currency bought less than the backtest assumed. The question then isn't whether you budgeted for inflation; it's whether you have a genuinely flexible major category. Travel that can be deferred, housing that can be downsized, discretionary spending that can shrink by twenty percent without eliminating quality of life—that's the margin that absorbs the gap between measured and lived inflation. If your budget is mostly non-discretionary costs in categories inflating faster than CPI, you don't have that margin.
If debasement is the mechanism Alden describes, then a portfolio plan that depends on currency stability is a plan with a built-in assumption you can't stress-test. The question isn't what withdrawal rate survives backtest—it's whether your actual spending can bend when the dollar stretches.