Bernie Sanders is gaining on Democratic front runner Hillary Clinton, according to a new Fox News poll released Sunday which shows his support has more than doubled since June, when the same poll showed him at 15 percent.

The self-proclaimed socialist senator from Vermont is up to 30 percent in the national poll, conducted Aug. 11-13.

Meanwhile, Clinton, considered the prohibitive front-runner, has seen her support dip below 50 percent for the first time since she began running for office.

The former secretary of state's presumed inevitability has been called into question recently, as she's faced increased questions about her management of a private email server during her tenure at State.

The poll contains evidence that public concern about the emails is sapping Clinton's support. A majority of respondents, 58 percent, said that they believe Clinton knowingly lied when she claimed that there was classified email on her private server. A smaller majority said that she put the country's security at risk by mishandling classified emails.

At the same time as Hillary's support wanes, Sanders' campaign has filled up arenas across the country, drawing attention to his liberal agenda.

The poll placed support for Vice President Joe Biden, who is reported to be contemplating a run, at 10 percent.

Former Maryland Gov. Martin O'Malley and former Virginia Sen. Jim Webb, both declared candidates, garnered 1 percent in the poll.

The Fox News poll involved 1,008 registered voters and has a margin of error of three percentage points.

Despite the results from Sunday's poll, Clinton still has a 32.5 percentage point lead over Sanders in the RealClearPolitics average of polls.