Vice President Joe BidenJoseph (Joe) Robinette BidenOvernight Tech: FCC won't delay net neutrality vote | Google pulls YouTube from Amazon devices | Biden scolds social media firms over transparency Medicaid funds shouldn't be used to subsidize state taxes on health care Biden hits social media firms over lack of transparency MORE gave a closed-door speech Friday to South Carolina Democrats that included a shot at the Clintons.

Biden, a potential 2016 candidate, said the unraveling of middle-class financial security began in "the later years of the Clinton administration," not under George W. Bush, CNN reported Saturday.

Speaking for more than thirty minutes at the VIP Capital City Club event in Columbia, S.C., he addressed the prominant group of attendees in the key presidential primary state.

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In recent months, the vice president has focused on revving up liberals on issues of income inequality, as he prepares for a possible run against former Secretary of State Hillary ClintonHillary Diane Rodham ClintonGrassley blasts Democrats over unwillingness to probe Clinton GOP lawmakers cite new allegations of political bias in FBI Top intel Dem: Trump Jr. refused to answer questions about Trump Tower discussions with father MORE, though many Democrats don't think he'd run against her.

Biden did not mention his own presidential ambitions Friday, but multiple sources described his speech as "populist" and high-energy, according to CNN. One attendee said it was an "Elizabeth Warren-type speech" blasting income inequality.

"He said we have some of the most productive workers in the world, but corporations are more concerned about their stockholders than they are about their employees," one attendee said. "He talked about how the fruits of labor go to stockholders, rather than to the people who are producing it. That the people making the money in this country are the corporations."

Another attendee described it as "a stem-winding, almost revival-type speech."

Biden's rare rebuke of the Clintons' economic policies, which some liberals view as too friendly to Wall Street, indicates how he'd possibly approach a 2016 campaign if he and Clinton square off in a primary.

Last April, he delivered a lengthy attack on Rep. Paul Ryan's (R-Wis.) budget at George Washington University in his push to court liberal voters.

This post was updated at 10:40 a.m.