MF Global, the commodities brokerage that plunged into bankruptcy while headed by a prominent Democrat, has become a point of attack for Republicans in the battle over financial regulation.

“Unfortunately for the American people, more powers and more tools cannot help when regulators fail to do their jobs,” Sen. Richard C. Shelby (Ala.), the ranking Republican on the Senate Banking Committee, said at a hearing Tuesday.

Shelby accused a top regulator and Obama appointee of dodging questions, and he needled the Commodity Futures Trading Commission for not being able to track down more than $1 billion of customer funds that he said remained missing 37 days after MF Global’s bankruptcy filing.

“It’s unclear how much longer customers must wait while a bewildered CFTC searches for their money,” Shelby said. “The victims of MF Global, I believe, deserve better.”

The MF Global issue arose during a hearing to review implementation of the Dodd-Frank Act, which was enacted last year to tighten financial regulation in response to the 2008 crisis. Republicans overwhelmingly opposed the regulatory expansion. Since then, many have resisted moves to implement the new law, including the creation of a consumer financial protection bureau. Some say regulators don’t need more powers; they just need to do a better job.

MF Global was headed by Democrat Jon S. Corzine, who was formerly governor of New Jersey, a U.S. senator and chief executive of Goldman Sachs. The firm bet heavily and unsuccessfully on European government bonds. Though the firm was required to keep customers’ funds separate from its own, a trustee overseeing its liquidation recently estimated that $1.2 billion or more could be missing from clients’ accounts.

CFTC Chairman Gary Gensler, who worked under Corzine at Goldman Sachs, initially took part in the CFTC’s review of MF Global but recused himself after critics, such as Sen. Charles E. Grassley (R-Iowa), raised questions about his relationship with Corzine. At the time, Grassley said it appeared that Gensler should recuse himself from the case.

“It’s hard to see how the commission chairman could be completely objective in looking out for wronged investors when he has such strong ties to the principal of the failed firm,” Grassley said then.

At Tuesday’s hearing, Gensler said he withdrew when it became an enforcement case that could involve the investigation of individuals. He said he did not want to be a distraction, noting that Corzine had been his boss. Gensler said that CFTC staff members had told him that his recusal was not necessary.

Sen. Mike Johanns (R-Neb.) said he didn’t understand why Gensler would be a distraction: “To me it looks like you’re ducking the responsibilities of your job.”

Shelby said he has asked the trading commission’s inspector general to examine the agency’s oversight of MF Global, including whether Gensler should have recused himself earlier or at all.

Gensler referred some of the lawmakers’ questions about MF Global to CFTC Commissioner Jill E. Sommers, a Republican who is leading the agency’s work on the case. “We have not located all the funds that are missing,” Sommers said, adding that sorting out the firm’s finances has been “a very complicated process.”

The attention to MF Global isn’t entirely partisan. The Senate Agriculture Committee on Tuesday voted unanimously to subpoena Corzine for a Dec. 13 hearing.