Taxpayers will get their money back on AIG. My models suggest that Fannie and Freddie, on the other hand, are a gold mine. For $2 billion in cash up front and some $200 billion in loan guarantees so far, the U.S. government now controls $5.4 trillion in mortgages and mortgage guarantees.

Fannie and Freddie each own around $800 million in mortgage loans, some of them already at discounted values. They also guarantee the credit-worthiness of another $2.2 trillion and $1.6 trillion in mortgage-backed securities. Held to maturity, they may be worth a lot more than Mr. Paulson paid for them. They're called distressed securities for a reason.

You can slice the numbers a lot of different ways. My calculations, which assume 50% impairment on subprime loans, suggest it is possible, all in, for this portfolio to generate between $1 trillion and $2.2 trillion -- the greatest trade ever. Every hedge-fund manager will be jealous. Mr. Buffett is buying a small piece of the trade via his Goldman Sachs investment.

Over 10 years this could change the budget scenario in D.C., which can also strengthen the dollar. The next president gets a heck of a windfall. In the spirit of Secretary of State William Seward's purchase of Alaska for $7 million in 1867, this week may be remembered as Paulson's Folly.