Top officials from the Securities and Exchange Commission and the Commodity Futures Trading Commission are raising concerns about the Volcker rule. CFTC Chairman Gary Gensler says the rule fails to adequately crack down on proprietary trading. Kara Stein, a member of the SEC, says the proposal would allow banks to circumvent its purpose. The objections threaten to further delay the rule's implementation. Meanwhile, Federal Reserve Vice Chairwoman Janet Yellen wrote to Sen. Mike Crapo, R-Idaho, the ranking Republican on the Senate banking committee, that maybe banks should get more time to comply with the rule.