For the Democrats who pushed the rule through, it could be the start of a return to the days of pre-2008 excess. To the new Trump administration, and to much of the the financial sector, it would be a bonfire of red tape needed to let the economy grow again. Who’s right? The short answer is that no one has a monopoly on rightness here. But here’s what you need to know.

Q. What is the Volcker Rule?

A. Section 619 of the Dodd-Frank Wall Street Reform and Consumer Protection Act (to give it its proper name) aims to stop the use of customer deposits by banks for risky or speculative purposes. Specifically, it bans such banks from trading on their own accounts in almost all securities such as bonds and stocks, and from investing in hedge funds or private equity firms. The rule is named for former Federal Reserve Chairman Paul Volcker, who originally proposed it.

Why and when was it introduced?

After the financial crisis and the huge taxpayer-funded bailouts of 2008, and the Great Recession that followed them, Congress wanted to stop practices that it thought had contributed to the Financial Crisis. Many parts of Dodd-Frank aimed at reducing banks’ overall risk profile—for example, by imposing higher minimum levels of capital. Others, like the Volcker Rule, aimed at reducing risks by simplifying bank structures to make them more transparent and to reduce the conflicts of interest that arise when one division of a bank (such as its retail operations) has different priorities from, say, the high-flying investment banking types. It came into effect in 2015, after around five years of haggling.

Didn’t we once have a law that did the same thing?

Indeed we did. After the 1929 crash, Congress passed the Glass-Steagall Act which strictly separated retail and commercial banking from the securities and investment business. Its repeal in 1999 under Bill Clinton allowed the formation of such “universal banking” giants such as Citigroup and J.P. Morgan Chase. Glass-Steagall is now back in the news because Gary Cohn, President Donald Trump’s top economic adviser (and Goldman Sachs alum), reportedly backed a return to such a segregated banking industry at a meeting with senators earlier this week.

Why do we need a new Glass-Steagall rather than the existing Volcker Rule?

Cohn’s remarks were only reported second-hand, so it’s not clear what his logic is. However, the general aim of the administration is to scrap the parts of Dodd-Frank that aren’t working as planned, i.e., the parts it believes aren’t really making the system any safer, and the parts that are getting in the way of sound, healthy lending.

And the Volcker Rule is one of those things?

Many bankers—and not just those on Wall Street—think so. When even Daniel Tarullo is admitting the need for change, then the rule is probably on the way out.

Who?

Daniel Tarullo was until today the Federal Reserve’s point man for regulation. In a final speech on Wednesday, he acknowledged three main problems:

1. The Volcker Rule covers way more banks than it was intended to, imposing unnecessary costs on community banks which don’t do speculative trading.

2. It appears to have frightened banks out of making markets in key sectors of financial markets such as corporate bonds. This makes it more expensive for companies to raise money through the bond market (a point made at length and repeatedly by the U.S. Chamber of Commerce).

3. It’s impossible to enforce legally, inasmuch as it requires supervisors to guess what was going through bankers’ minds when they made particular trades—was it legitimate market-making? Or was it speculation?

What is the difference?

There are as many answers to that as there are market-makers. Nobody disputes that market-makers are vital in ensuring the smooth flow of capital to where it’s needed. But holding inventory for market-making inevitably puts your own capital at risk. In any event, Tarullo’s comments suggest that the Fed has given up trying on that score.

Oh. Is That All?

By no means. J.P. Morgan Chase CEO Jamie Dimon–

–I might have known he’d have something to say about it …

–Let me finish. Dimon wrote in his annual letter to shareholders this week that the real problem with the Volcker Rule is that is that it is overseen by five separate regulators, grouped together in the Financial Supervisory Oversight Council. This “leads to slow rulemaking, excessive reporting and varied interpretations on what the actual rules are,” the last issue being made even worse by the fact that the FSOC has no enforcement powers.

So has it failed?

That would be too harsh. The kind of big-money proprietary bets that Wall Street banks were making before the crisis have largely migrated to the hedge fund and private equity business, which is where the regulation said they belonged. But it has had unintended consequences, and taken together they may outweigh the benefits of keeping the Volcker Rule in its present form.

CORRECTION: the original version of this story incorrectly referred to the FSOC as the Federal Supervisory Oversight Committee.