The remarks drew condemnation from the Obama campaign, who said Booker was wrong to defend Romney's tenure at Bain.

"In this particular instance, he was just wrong," senior campaign strategist David Axelrod told CNN.

Booker later scrambled to reverse course, releasing an online video saying Romney's record was fair game and expressing his disappointment in the GOP's "I'm with Cory" web campaign.

An aide to Booker told the Star-Ledger that Torres's departure was not related to fallout from the controversy.

"It has been a pleasure to serve in this administration for six years, and as a Newarker, there is no greater reward than to work for the city that you love," Torres said in a statement. "I’ve had the opportunity to work with an amazing team, and wish the mayor the best."