John McCain has made it clear this week he doesn't understand what's happening on Wall Street any better than Barack Obama does. But on Thursday, he took his populist riffing up a notch and found his scapegoat for financial panic -- Christopher Cox, the chairman of the Securities and Exchange Commission.

To give readers a flavor of Mr. McCain untethered, we'll quote at length: "Mismanagement and greed became the operating standard while regulators were asleep at the switch. The primary regulator of Wall Street, the Securities and Exchange Commission (SEC) kept in place trading rules that let speculators and hedge funds turn our markets into a casino. They allowed naked short selling -- which simply means that you can sell stock without ever owning it. They eliminated last year the uptick rule that has protected investors for 70 years. Speculators pounded the shares of even good companies into the ground.

"The chairman of the SEC serves at the appointment of the President and has betrayed the public's trust. If I were President today, I would fire him."

Wow. "Betrayed the public's trust." Was Mr. Cox dishonest? No. He merely changed some minor rules, and didn't change others, on short-selling. String him up! Mr. McCain clearly wants to distance himself from the Bush Administration. But this assault on Mr. Cox is both false and deeply unfair. It's also un-Presidential.

Take "naked" shorting, in which an investor sells a stock short -- betting that it will fall in price -- without first borrowing the shares he is selling from an investor who owns them. The SEC has never condoned the practice, and since 2005 it has clamped down on short selling in any stock that shows evidence of naked shorting. The SEC further tightened its rules against naked shorting just hours before Mr. McCain excoriated Mr. Cox for doing nothing.