Vice President Joe Biden revealed the vote he regretted most during a speech on the financial sector at Georgetown University Monday. He said his vote to repeal the Glass-Steagall Act in 1999 was "the worst vote I ever cast in my entire time in the U.S. Senate."

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"This was a debate inside the White House about whether I should say this," Biden said. "But I've never not said what I believe."

He said the repeal of Glass-Steagall, also known as the Banking Act of 1933, a law that prohibited commercial banks from operating as investment banks, "allowed banks with deposits to take on risky investments, putting the whole [financial] system at risk." Congress passed Glass-Steagall in the midst of the Great Depression, in 1933, as an attempt to safeguard the financial sector.

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In 1999, then-Delaware Sen. Biden and 89 other senators voted to enact the Gramm-Leach-Bliley Act — a law that effectively overturned Glass-Steagall, repealing measures that "allowed the rise of several very large banks in the United States with business lines that cut across both commercial lending and securities business," The New York Times reported. Financial experts have linked the repeal of Glass-Steagall to the 2008 recession, which was revisited during the 2015 Democratic primaries.

Vermont Sen. Bernie Sanders criticized its repeal in contrast to former Secretary of State Hillary Clinton, who argued that its relevance to the 2008 financial crisis was overemphasized.

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"Today, not only must we reinstate this important law, but if we are truly serious about ending too big to fail, we have got to break up the largest financial institutions in this country," Sanders said in a July 2015 statement. Sanders was "one of eight senators in 1999 who voted against its repeal," The Hill reported.