There are warnings that belong to the realm of theory, and others that carry the quiet weight of experience. When Henry Paulson speaks about a potential collapse in demand for US Treasuries, it is not an academic exercise. It is a man who once stood at the centre of a financial storm, now describing a different one, less visible, but potentially more dangerous. Because this time, the fire would not come from the banks. It would come from the state itself. Paulson’s message is disarmingly simple. The United States must prepare a contingency plan for the day when investors begin to doubt, not the strength of its economy, but the sustainability of its debt. Not a liquidity crisis, as in 2008, but a crisis of confidence. And confidence, in sovereign markets, is a far more fragile currency than liquidity.

The uncomfortable truth is that the United States still enjoys a privilege no other country possesses. It issues the world’s reserve currency. It controls the deepest and most liquid bond market on the planet. It can absorb shocks that would crush others. For now, that privilege still holds. But it is no longer unquestioned. Behind the reassuring narrative of American resilience lies a more awkward arithmetic. Federal deficits have averaged around 6% of GDP in recent years, a level historically reserved for wars or recessions, now becoming structural. Debt is on a trajectory to exceed 100% of GDP and continue rising. Interest payments are no longer a marginal cost, they are becoming a central one. The machine still runs, but it is increasingly financed by itself. And that is where the risk begins to take shape. A sovereign debt crisis in the United States would not look like past crises. There would be no sudden collapse of a banking system to rescue, no straightforward intervention to stabilise credit markets. There would be a more insidious dynamic, one Paulson describes with unusual clarity: a market where demand weakens, yields rise, prices fall, and the cost of servicing the debt accelerates the very deficit that caused the problem in the first place.

A loop. Slow at first. Then brutal. In such a scenario, the Federal Reserve would stand as the buyer of last resort. Not as a choice, but as a necessity. And that is where the line between monetary policy and fiscal survival would finally disappear. When a central bank is forced to absorb sovereign issuance not to stabilise markets but to ensure the state can continue to finance itself, the system has already entered a different regime. Paulson does not pretend to know when such a moment could arrive. That is precisely the point. Sovereign crises do not announce themselves in advance. They emerge when the marginal buyer hesitates, when the auction clears at a higher yield than expected, when confidence shifts not dramatically, but incrementally, until it suddenly is not there anymore. What makes the situation more paradoxical is that, in the short term, the United States appears stronger than its rivals. Its economy is dynamic. Its corporate sector remains powerful. Its energy independence offers a degree of insulation from geopolitical shocks such as the war in Iran. Compared to China, whose growth remains structurally unbalanced, or to Europe, which struggles with weak momentum, the United States still looks like the cleanest shirt in a very dirty laundry basket.

But even Paulson is careful to draw the distinction. America’s strength is not the issue. Its discipline is. The real constraints are political. Reducing the deficit requires a combination of higher revenues and controlled spending. It implies tax increases, the removal of fiscal loopholes, and reforms to social security and healthcare programmes that are both economically necessary and politically toxic. None of this is new. All of it is well understood. And none of it is happening. Because in Washington, as Paulson notes with understated irony, difficult decisions are rarely taken without an immediate crisis. This is the deeper fragility of the US system today. Not that it lacks the resources to stabilise its debt trajectory, but that it lacks the political coherence to act before the market forces its hand. Fiscal policy drifts. Polarisation paralyses. The deficit persists not because it must, but because it is easier to tolerate than to confront. And so the system moves forward, supported by habit, by inertia, and by the enduring belief that US Treasuries remain the ultimate safe asset. Until the day they are not.

That day may be distant. It may never come in the dramatic form some fear. The dollar’s dominance, the depth of US markets, and the absence of credible alternatives all argue for a slow erosion rather than a sudden break. But erosion, in sovereign finance, is often more dangerous than collapse. It is less visible, less urgent, and therefore less likely to provoke action until it is too late. Paulson’s warning is not that the United States is on the brink. It is that the margin for error is narrowing. The tragedy of such situations is always the same. The solution is known well in advance. The tools are available. The capacity exists. What is missing is not knowledge, but timing. Acting early is politically painful. Acting late is economically brutal. For now, the United States continues to borrow, to spend, and to reassure itself that demand will remain. And perhaps it will. But sovereign markets do not collapse because a country becomes weak. They collapse because, one day, they stop believing that strength will be enough.