Standard & Poor’s decision to downgrade the long-term outlook for U.S. sovereign debt came as a shock. It shouldn’t have. Credit-rating agencies (CRAs) such as S&P are a government-chartered cartel, with constraints on competition and a customer base guaranteed by statute. They are the sleepy backwaters of the financial world — and they are always the last to know. As one investment strategist put it to me this morning: We’ve been watching this train go by for a while now, and this is the caboose.

The textbook example of this is the case of Enron. All of the credit-rating agencies had Enron rated like stacks of solid gold until a few weeks before Jeff Skillings’s financial underpants finally hit his ankles. But long before the CRAs woke up, the markets had driven Enron’s stock price down to almost nothing. The ratings agencies aren’t the opening act — they’re the fat lady sweating out the final aria in our national fiscal Götterdämmerung.

A little over a year ago, the markets already were telling us that the government’s story about how it is finally going to fix its finances is pure fiction. Yields on U.S. Treasury bonds went higher than those on a number of blue-chip corporate bonds, leading your obedient servant to remark:

Who has better credit than Uncle Sam? If you ask the bond market, that elite list includes Berkshire Hathaway, Procter & Gamble, Lowe’s, Johnson & Johnson, and a host of other blue-chip corporate borrowers. The U.S. government has the ability to levy taxes on the largest national economy in the world, a vast and fearsome revenue-collection apparatus, and more than two centuries of constitutional government under its belt. P&G has Tampax.

As in the case of Enron, the smart money gets gone long before credit downgrades start hitting the headlines. As noted in this column, PIMCO, the world’s largest bond fund, got clear of U.S. Treasuries some time ago, following the lead of a number of hedge funds. The oil-exporting countries are dumping U.S. debt, too. Perhaps they know something we don’t?

Actually, they know something we do: Nothing about this is a secret. In the phrase adopted by Rep. Paul Ryan, what is coming is the most predictable economic crisis in our history: a nominal national debt of more than $14 trillion, a real national debt ten times that, and Barack Obama standing between the reformers and the needed reforms with a veto pen and excellent chances of being reelected in 2012. This isn’t sophisticated macroeconomic analysis; this is that anvil falling out of the sky onto the head of Wyle E. Coyote, and you don’t have to be a super-genius to figure out that it’s going to hurt like hell when it hits him. Even S&P gets that.

And that’s probably the reason this announcement hasn’t really sent big-time shock waves through the markets: It’s just confirming what everybody already knows: Washington’s finances are Enron writ large.

But unlike Enron, Washington has the power to tax, the power to print money, and an executive able to resist financial realities for a remarkably long period of time. Thus we have Obama administration officials lashing out at S&P today — as though it were the agency’s fault that Obama delivered an entirely implausible speech about deficit-control last week. Austan Goolsbee declared: “I don’t think that the S&P’s political judgment is right.” (What about their financial judgment?) Taking the prize for mealy-mouthed politics-speak is Treasury official Mary Miller, who said, “We believe S&P’s negative outlook underestimates the ability of America’s leaders to come together to address the difficult fiscal challenges facing the nation.” Never mind the vacuousness of her claim and the banality of her language — “come together,” indeed — did she not watch the president’s speech last week? Because he made it pretty clear that coming together with fiscal reality is not on his agenda, never mind coming together with Republicans to do something about the entitlement bomb or even discretionary spending. Look for more kill-the-messenger rhetoric from the Obama administration as the meltdown heats up.

Here’s the thing to watch: Nobody really knows what interest rate the bond market is going to demand to finance U.S. debt in the future. Right now, the Fed is buying most of the bonds Treasury puts up for sale, and simply printing money to do that. This “quantitative easing” is scheduled to end this summer, at which point Washington will find out what it is really going to cost to finance its debt. In FY2010, we spent $164 billion just on interest payments on the debt — up 18 percent from the year before. And that’s at historically low interest rates. If rates should go back up to their 1970s or 1980s levels, we could easily end up spending more on debt service than we spend today on big-ticket items like Medicare or national defense. That’s the hidden landmine on our national balance sheet: We don’t have to be worried only about the trillions of dollars in new debt that Obama proposed to load upon our backs, but also about what that proposal is going to do to the cost of paying interest on the debt we already have. We already know that we cannot afford the new debt that Obama would have us endure, but the real crisis will come when we find out that we cannot afford the debt we already have.

—  Kevin D. Williamson is a deputy managing editor of National Review and author of The Politically Incorrect Guide to Socialism, just published by Regnery. You can buy an autographed copy through National Review Online here.