Specifically, Mr. Geithner will have to turn over to Standard & Poor's evidence related to a telephone conversation he had with the CEO of S&P's parent company, McGraw Hill. In 2011, after S&P stripped the U.S. of its triple-A credit rating, Mr. Geithner met with President Obama in the Oval Office. McGraw Hill CEO Harold McGraw III says Mr. Geithner then called and told him that "you have done an enormous disservice to yourselves and to your country," and that S&P's conduct would be "looked at very carefully."

The Justice Department later sued S&P for $5 billion over the credit-rating firm's flawed opinions on mortgage bonds. But Justice never sued other companies that issued equally bad opinions. S&P says it was singled out as political payback for the downgrade. And based on Mr. Geithner's telephone threat, last month Judge Carter concluded the government should start turning over documents. Mr. Geithner recently asked the judge to quash a subpoena from S&P, citing cases in which judges had protected federal officials from having to provide documents and sit for depositions.

But Judge Carter denied Mr. Geithner's motion, saying S&P hasn't yet requested a deposition and that its requests are appropriately narrow. We hope the judge allows depositions under oath and full discovery to determine if this lawsuit is as political as it sounds.