Last week’s announcement that JPMorgan Chase, the big Wall Street bank, lost $2 billion in risky derivative trading activities should return attention to financial-reform regulation.

The news also should focus scrutiny on efforts by Wall Street banks to weaken provisions of the Dodd-Frank financial-reform law passed by Congress after the financial crisis.

When Dodd-Frank was passed by Congress, many people assumed reforms were now in place to curtail risky investments by Wall Street banks. But despite the law’s passage, many details are still being worked out by regulators — and the big banks, including JPMorgan Chase, have been lobbying for only minimal intervention in their risky, but normally profitable, trading activities.

Thursday’s admission of $2 billion in trading losses, made public by JPMorgan Chase CEO Jamie Dimon, should cast public attention on what the Dodd-Frank law can do — or cannot do — to prevent major banks from engaging in risky financial bets, once details of its implementation are completed.

Even though passed last year, the law’s new rules related to risky derivative trading by big banks were not scheduled to go into effect until the end of this year. And as those aspects of the law are being developed by regulators, big banks, including JPMorgan Chase, have been lobbying to dilute the law’s power to limit their trading activity.

JPMorgan Chase is the largest bank in the United States and suffered smaller problems than other investment banks in the financial crisis. As the model for modern banking and risk management, JPMorgan Chase and the well-connected and outspoken Dimon had been held up as reasons for regulators to resist tough new restrictions on banks. No more.

Last week’s report of $2 billion in losses from the company’s London operation gives plenty of ammunition to those who want to see tougher regulations. Already, Dimon has softened his opposition to tougher regulations in Dodd-Frank.

Tougher regulations on risky trading should only be the start of the conversation regarding financial reforms. There should be further debate over what “too big to fail” means and how Dodd-Frank would deal with a major bank, like JPMorgan Chase, if its risky investments threatened its existence or the health of the larger financial sector.

“Too big to fail” was a widely used term during the height of the financial crisis as jusification for actions to prop up troubled banks until they were stabilized.

The $2 billion loss is not expected to pose a major threat to JPMorgan Chase or the banking industry, but it is a warning that risky bank investments can go bad — and in a big way.

Another part of the renewed debate over financial reforms should examine the impact of allowing major banks with federal insurance on their deposits to engage in risky investments and derivative trading.

Following the Great Depression, those two functions were separated by the Glass-Steagall Act, passed in 1933. But that law was repealed by Congress in the late 1990s at the urging of the Clinton administration, which argued that big banks needed the change to compete in a now-global world of finance.

A part of the Dodd-Frank law, the so-called Volcker Rule, was designed to limit the kind of risky proprietary trading that was part of the financial crisis.

Both political parties are to blame for the loosened regulations that let the big Wall Street banks engage in risky financial bets. Wall Street banks have donated hundreds of millions of dollars to leading members of Congress, of both parties. And President Barack Obama raised record contributions from Wall Street in his 2008 campaign.

Wall Street’s influence over Washington also is linked to a revolving door that sees top bank executives work in Washington as regulators or Treasury Department officials, then, after serving in government, they return to Wall Street with powerful connections and influence.

Passage of the Dodd-Frank law gave the public the impression that reforms to prevent another financial crisis were in place. Last week, JPMorgan Chase revealed that not enough has changed since the banking crisis began several years ago.

JPMorgan Chase’s big losses from risky bets announced last week should be seized by Congress as an opportunity to revisit financial reform and tighten regulations, adopting a new approach to banks that were too big to fail three years ago and now are even bigger.