Do we need to go back to the drawing board?

“Here’s the key word in the rules: ‘exemption,’ ” former Senator Ted Kaufman, Democrat of Delaware, told me. “Let me tell you, as soon as you see that, it’s pronounced ‘loophole.’ That’s what it means in English.” Mr. Kaufman, now teaching at Duke University School of Law, earlier proposed a tougher version of the Volcker Rule, which was voted down in the Senate. “We’ve been through this before,” he said. “I know these folks, these Wall Street guys. I went to school with them. They’re smart as hell. You give them the smallest little hole, and they’ll run through it.”

“I support the concept of the Volcker Rule,” Representative Peter Welch, Democrat of Vermont, said, “but these rules aren’t going to be effective. We’ve taken something simple and made it complex. The fact that it’s 300 pages shows the banks pushing back and having it both ways.”

And these are Democratic critics of the proposed regulations. An overwhelming number of Republicans oppose them, as they have virtually every aspect of Dodd-Frank. Even Senator Richard Shelby, Republican of Alabama, the ranking member of the Senate Committee on Banking, Housing and Urban affairs, who was the lone Republican to support the tougher Brown-Kaufman legislation, dismisses the latest incarnation.

“This proposal, however, is filled with central questions that Congress should have answered before even drafting Dodd-Frank,” said Jonathan Graffeo, a spokesman for Senator Shelby. “Instead, Congress willfully ignored the ramifications of its actions, just as it did in repealing Glass-Steagall.”

Yet the Volcker Rule, or something like it, could be the most important reform measure to emerge from the financial crisis.

If there was any doubt about that, this week the Securities and Exchange Commission unveiled its latest charges involving mortgage-backed securities. In what may be a new low for conduct by a major Wall Street firm in the walk-up to the financial crisis, Citigroup settled charges (without admitting or denying guilt) that it defrauded investors by creating a package of mortgage-backed securities for which it selected a pool of mortgages likely to default, bet against the security for the bank’s benefit by shorting it and then foisted it off on unwitting investors without disclosing any of this.

According to the S.E.C., one trader characterized this particular security in an all-too-candid e-mail as “possibly the best short EVER!”