Elizabeth Warren is making good on her promise to scare Wall Street. Today, she'll introduce a bill to reenact Glass-Steagall.

Glass-Steagall is the 1933 law that separated commercial and investment banking. Back in 1999 it was repealed by the Gramm-Leach-Bliley Act at the urging of Wall Street heavyweights like then-Citi CEO Sandy Weill.

Then the financial crisis happened. Many banks failed and others got swallowed up into larger banks.

After all that, Sandy Weill said he was wrong on national television.

Elizabeth Warren was elected to the Senate based in part on her crusade against Wall Street excess. For many, this is one massive way to do that. Sen. John McCain (R-Ariz), Washington Democrat Maria Cantwell and Maine Independent Angus King are co-sponsoring the bill.

You can read it in full here, but the introduction follows:

To reduce risks to the financial system by limiting banks’ ability to engage in certain risky activities and limiting conflicts of interest, to reinstate certain Glass-Steagall Act protections that were repealed by the Gramm-Leach-Bliley Act, and for other purposes.

This is a move to reduce the size of America's behemoth banks. We've heard the slogans not just from Warren, but also Senators David Vitter (R-LA) and Sherrod Brown (D-OH)— "too big to fail," "too big to manage."

Wall Street's army of lobbyists are unlikely to let this stand without an epic fight. Let them march; Warren loves being a conversation starter, and she'll repeat this one over and over again.

Read the full statement from Warren's office below:

Washington, DC - Senators Elizabeth Warren (D-MA), John McCain (R-AZ), Maria Cantwell (D-WA), and Angus King (I-ME) today will introduce the 21st Century Glass-Steagall Act, a modern version of the Banking Act of 1933 (Glass-Steagall) that reduces risk for the American taxpayer in the financial system and decreases the likelihood of future financial crises.

The legislation introduced today would separate traditional banks that have savings and checking accounts and are insured by the Federal Deposit Insurance Corporation from riskier financial institutions that offer services such as investment banking, insurance, swaps dealing, and hedge fund and private equity activities. This bill would clarify regulatory interpretations of banking law provisions that undermined the protections under the original Glass-Steagall and would make "Too Big to Fail" institutions smaller and safer, minimizing the likelihood of a government bailout.

"Since core provisions of the Glass-Steagall Act were repealed in 1999, shattering the wall dividing commercial banks and investment banks, a culture of dangerous greed and excessive risk-taking has taken root in the banking world," said Senator John McCain. "Big Wall Street institutions should be free to engage in transactions with significant risk, but not with federally insured deposits. If enacted, the 21st Century Glass-Steagall Act would not end Too-Big-to-Fail. But, it would rebuild the wall between commercial and investment banking that was in place for over 60 years, restore confidence in the system, and reduce risk for the American taxpayer."

"Despite the progress we've made since 2008, the biggest banks continue to threaten the economy," said Senator Elizabeth Warren. "The four biggest banks are now 30% larger than they were just five years ago, and they have continued to engage in dangerous, high-risk practices that could once again put our economy at risk. The 21st Century Glass-Steagall Act will reestablish a wall between commercial and investment banking, make our financial system more stable and secure, and protect American families."

"Too many Main Streets across America have paid the price for risky gambling on Wall Street," Senator Maria Cantwell said. "This bill would restore clear bright lines that separate risky activities from the traditional banking system. It's time to restore faith in our financial institutions by rebuilding the firewall that protected our economy for decades in the wake of the Great Depression. Restoring Glass-Steagall would focus our financial system where it belongs: getting capital into the hands of job creators and businesses on Main Streets across America."

"As Maine families continue to feel the sting of the 2008 economic downturn, America's largest financial institutions continue to engage in risky banking and investment activities that threaten the health of our financial sector and our economy as a whole. While recent efforts at financial sector regulatory reform attempt to address the ‘too big to fail' phenomenon, Congress must take additional steps to see that American taxpayers aren't again faced with having to bail out big Wall Street institutions while Main Street suffers," Senator Angus King said. "While the 21st Century Glass-Steagall Act is not the silver bullet to end ‘too big to fail,' the legislation's re-establishment of clear separations between retail and investment banking, as well as its restrictions on banking activities, will limit government guarantees to insured depository institutions and provide strong protections against the spillover effects should a financial institution fail."

The original Glass-Steagall legislation was introduced in response to the financial crash of 1929 and separated depository banks from investment banks. The idea was to divide the risky activities of investment banks from the core depository functions that consumers rely upon every day. Starting in the 1980s, regulators at the Federal Reserve and the Office of the Comptroller of the Currency reinterpreted longstanding legal terms in ways that slowly broke down the wall between investment and depository banking and weakened Glass-Steagall. In 1999, after 12 attempts at repeal, Congress passed the Gramm-Leach-Bliley Act to repeal the core provisions of Glass-Steagall.