(Bloomberg) -- Alex Oh, who was named head of the Securities and Exchange Commission’s vaunted enforcement division last week, abruptly resigned, an early setback for Gary Gensler’s tenure running the Wall Street regulator.

The surprise move, announced Wednesday in an SEC statement, means Gensler won’t have his preferred pick leading what’s arguably the agency’s most important division. Melissa Hodgman, who was previously serving as acting director of the enforcement unit, will return to that role, the SEC said.

Before joining the SEC, Oh was a partner at Paul, Weiss, Rifkind, Wharton & Garrison. At Paul Weiss her corporate clients included Exxon Mobil Corp. In a matter representing Exxon, Oh said her opposing counsel was “agitated, disrespectful, and unhinged” during a deposition without providing evidence, according to an April 26 order. That prompted a judge to question why he shouldn’t sanction Oh, the order shows. Bloomberg News couldn’t immediately determine what the Exxon case was about.

“A development arose this week in one of the cases on which I worked while still in private law practice,” Oh said in an emailed resignation to Gensler reviewed by Bloomberg. “I have reached the conclusion that I cannot address this development without it becoming an unwelcome distraction.”

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