The American dollar is in the midst of a large fall in its value, or depreciation, as measured against other major currencies. The decline has been steady since 2002 and our currency is down about 35 percent from that peak. After strengthening slightly more than 10 percent during the global financial crisis of the past 18 months, the dollar is again falling back toward its pre-crisis lows, representing its weakest international value since 1967.

But there is a definite possibility that the dollar could soon decline further or faster.

At the level of general economic strategy, the American government has responded to a financial sector crisis with an expansionary fiscal policy, and the Federal Reserve is implementing loose monetary policy. Andrew Haldane, responsible for financial stability at the Bank of England, puts it this way:

“For the authorities, [excessive risk-taking by the financial sector] poses a dilemma. Ex-ante, they may well say “never again.” But the ex-post costs of crisis mean such a statement lacks credibility. Knowing this, the rational response by market participants is to double their bets. This adds to the cost of future crises. And the larger these costs, the lower the credibility of “never again” announcements. This is a doom loop.” (link to the paper)

In addition to a financial crisis, we also have a large current account deficit, meaning that we buy more from the world than we sell. The deficit was $100 billion in the latest available (second quarter) data, which is around 3 percent of gross domestic product, and we finance that with capital inflows from abroad. (The current account deficit is down from around 6 percent, but two-thirds of the decline is due to the lower price of oil).

In the past, many of those inflows have been private investments of various kinds, but as investors around the world question whether United States government debt, and its dollars, are really worth the paper, it is increasingly difficult for us to finance our deficit with the outside world.

What does this mean for the dollar?

Treasury Secretary Timothy F. Geithner continues to repeat that a strong dollar is “very important” for the American economy, but United States fiscal and monetary policy pushes toward depreciation. To bail out our banks, we need cheap money, and this implies some inflation. To finance our current account deficit, investors need to think they are buying inexpensive assets from us. Everything points to a cheaper dollar. (The same thing is happening in Britain, but the Bank of England is increasingly explicit about this point and the unsavory broader situation.)

A “hard landing” scenario for the dollar could be painful.

The 1980s classic, Stephen Marris’s “Deficits and the Dollar: The World Economy at Risk,” stresses that a rapidly falling dollar would push up United States inflation, resulting in higher interest rates and a deep recession (pp. lx-lxi). Writing in the latest edition of Foreign Affairs, Fred Bergsten emphasizes that such outcomes are still possible today. A weakening dollar will cause inflation fears, so yields on long-term government bonds will rise to compensate investors for inflation, and we will need to pay more and more to finance our large debts.

The idea that the American dollar might follow emerging markets such as Russia in 1998 and Argentina in 2002, or Britain in the 1970s — and so depreciate by 50 percent or more in a relatively short time — is certainly implausible now. But such a “doom scenario” is not unrealistic in the future without change.

In this context, the American government needs to control its budget deficit to keep this adjustment on track, and to stop confidence in the dollar from falling further. Our government collects far too little in taxes for what it spends. There is no choice but to raise taxes soon and rein in spending.

Short-term rates (controlled by the Fed) will stay low, while long-term rates (market-determined and affected by trust in our Treasury and Fed to keep the value of dollar strong) will rise as people fear their dollar investments will be debased. There is no doubt that both the Fed and the Bank of England know what is happening. The spread between short- and long-term rates (known as the “yield curve”) will rise, and banks will benefit; would-be home buyers and people with overdrafts or outstanding credit card balances pay more, while savers get little.

This is how the public pays for the past losses of our financial system.

We don’t have to do this again and again. We could start by changing our financial system from the roots. We need to credibly remove the promise to bail out our large banks each time they fail. This means forcing them to hold more capital, dividing them up so they are smaller, and then letting them fail when they make poor gambles.

The Treasury’s past and current close connections to Goldman Sachs, Citigroup and other major investment banks illustrate how our own doom machine functions. We need to break up these “banks” so they are small enough to fail, and also ensure that no bank, regardless of its connections, is able to demand that the Fed and the Treasury support its solvency in the future to prevent financial collapse.

In this context, a weakening dollar helps the administration to put an unstable financial system back on its feet — and to crank up our “doom machine.”

By Peter Boone and Simon Johnson

This is a slightly modified version of a post that appeared this morning on the NYT Economix blog; it appears here with permission. If you wish to reproduce the entire post, please contact the New York Times.