TEXT OF STORY

SCOTT JAGOW: The agency that monitors Wall Street has a pretty good reputation for keeping its nose clean. The Securities and Exchange Commission would like to keep it that way, but today, the head of the SEC testifies before Congress. He'll face questions about stopping an investigation because the target had White House connections. More now from Scott Tong.

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SCOTT TONG: Last summer, Gary Aguirre was an SEC attorney. He suspected insider trading at a hedge fund involving John Mack, the CEO at Morgan Stanley.

Aguirre wanted to subpoena Mack, but he says higher-ups on the SEC staff said no 'cause Mack's a big-time fundraiser for the president. Soon after, SEC investigator Aguirre was fired.

It all puzzles Duke law professor James Cox.

He says SEC staffers have long been considered clean and apolitical.

JAMES COX: If there's any evidence of Congressional pressure to pull back on a enforcement investigation, this would put the SEC in the same class as the Chicago Black Sox scandal of years past.

An SEC in-house investigation found no dirty business, but last Thursday, the investigation was reopened. That same day the commission told John Mack it wanted to question him.

In Washington, I'm Scott Tong for Marketplace.