Senators Elizabeth Warren (D-Mass.), John McCain (R-Ariz.), Maria Cantwell (D-Wash.), and Angus King (I.-Me.) have reintroduced their “21st Century Glass-Steagall Act,” which would restore the historic division between traditional (or commercial) banking world and the casino world of trading and speculating. Five years after passage of the Dodd-Frank Act, the case for this bipartisan legislation is stronger than ever.

After this bill was introduced in the last Congress, nearly 600,000 Americans signed online petitions of support, while dozens of national, state and local organizations gave their backing to a joint letter making the case for its enactment.

While Dodd Frank has changed the financial system in positive ways, the biggest banks have only grown bigger since the financial crisis of 2008, and they continue to engage in large-scale financial speculation with the benefit of public subsidies and guarantees. When banking and trading activities are intermingled in this way, bankers face incentives to sacrifice the well-being of their customers in order to chase after short term gains for their institutions and themselves. That was true before the crisis, and it is still true today.

For more than half a century, the original Glass-Steagall Act – officially the Banking Act of 1933 – helped prevent the spread of financial instability from the trading markets to the rest of the economy. The breakdown of that barrier not only contributed to the financial meltdown, but also facilitated the current dominance of a small number of global mega-banks. Under Glass-Steagall, major investment banks such as Drexel Burnham and Salomon Brothers failed without creating serious contagion in the broader economy. In the post-Glass-Steagall world, the failure of investment banks such as Bear Stearns and Lehman threatened the entire economy.

By restoring the sharp line between commercial banking and trading, this legislation would make our financial system more secure and better able to support the real economy. The new bill also updates the old division in necessary ways. Even before the Gramm-Leach-Bliley Act, which formally repealed Glass-Steagall, administrative decisions by regulators such as the Federal Reserve and the OCC had seriously eroded the division between commercial and investment banking. That erosion was made possible by loopholes in the original Glass-Steagall statute. The new legislation adds clear prohibitions on commercial bank involvement in a range of dealer, trading, and derivatives market activities, while still preserving the ability to engage in traditional trust and fiduciary roles.