(Jin Lee/Bloomberg)

The market isn’t totally wrong, of course. The federal government probably won’t default on its debt. But it’s actually pretty hard to explain how we get the spending line and the revenues line to match each other. And we have a really dysfunctional political system. We’ll figure it out somehow. We always do. But our low borrowing costs are an advantage we want to preserve for as long as possible. That means keeping the market from realizing that partisan polarization mixed with our weird legislative system makes insane outcomes easily imaginable.

This is why a shutdown would be so dangerous. A last-minute deal tells the market that America is a country that dithers and procrastinates and anguishes but eventually makes the necessary decisions to avert terrible consequences. We can be trusted to follow through, even if only at the last minute. A shutdown tells the market that our political system has become so dysfunctional that we actually can’t be trusted.

Asger Lau Andersen, David Dreyer Lassen and Lasse Holbøll Westh Nielsen — remember them? — have looked into how the market treats late budgets in the states — and late budgets in the states, it should be noted, are considerably less public and psychologically disruptive than a shutdown of the federal government during a weak economy. The answer is: not kindly (pdf). “We estimate that a budget delay of 30 days has a long run impact on the yield spread between 2 and 10 basis points,” they conclude. To put that in context, economists estimated that if the Federal Reserve pumped $400 billion into the economy, it’d lower yield spreads by about 20 basis points, or two-tenths of a percent. And it actually gets worse than that: “Markets also punish late budgets much more harshly if they occur during times of fiscal stress.”

I think it’d be fair to characterize this as a time of fiscal stress, don’t you?

There are some reasons for optimism here. Markets seem to punish fiscal mismanagement more lightly if the state has access to lots of money, which usually means reserves. The federal government has access to lots of money — though through borrowing, not reserves — so it’s possible we’d get off lightly, too. If you look back to Treasury yields in 1995, you don’t see an obvious change, but (a) perhaps yields would have been lower without the shutdown and (b) the economy is a lot weaker today than it was in 1995. At any rate, do we really want to test this? And if so, how many times? The tea party types are already promising to oppose an increase in the debt ceiling in the absence of massive entitlement cuts. Sen. Marco Rubio says he’ll oppose lifting the debt ceiling unless it’s accompanied by “a plan for fundamental tax reform, an overhaul of our regulatory structure, a cut to discretionary spending, a balanced-budget amendment, and reforms to save Social Security, Medicare and Medicaid.” That’s quite a list of demands in order to avoid economic catastrophe.

The irony of all this comes clear if you consider why we’re afraid of deficits in the first place. If the market comes to believe our debt is too large for our political system to pay back, they’ll become more skittish about buying government debt, and that’ll send interest rates higher and the economy lower. But if we have a series of shutdowns while we argue over how much to cut and how fast, our paralysis will convince the market we can’t get our act together in time to pay off our debts and they’ll send interest rates skyrocketing anyway. We’ll have caused exactly what we sought to prevent, and done it now, when the economy is weak, rather than later, when the economy is stronger. As I said at the beginning of this piece, I’d sure hate to be known for causing an economic crash. How about you, Congress?