Bernie Sanders has taken a narrow lead over Hillary Clinton in Iowa more than four months before the state’s caucus, according to a poll released Thursday.

The Vermont senator is favorite among 41% of Iowa likely Democratic participants, compared with 40% supporting the former Secretary of State, according to a Quinnipiac poll released Thursday. That marks a major reversal from early July, when Clinton was ahead of Sanders, 52% to 33%.

Sanders, an anti-establishment candidate who has made economic inequality the rallying cry of his campaign, has surged in polls throughout the summer, benefiting from discontent among Democratic voters. Clinton, meanwhile, has suffered as a result of the controversy over her private email server.

“Sanders has seized the momentum by offering a message more in line with disproportionately liberal primary and caucus voters,” said Peter A. Brown, assistant director of the Quinnipiac University Poll. “He is the candidate of the Democratic left, against his own party’s bosses and their prized presidential candidate, Secretary Hillary Clinton.”

Sanders is also polling ahead of Clinton in New Hampshire, the second Democratic nominating contest.

MORE: How Bernie Sanders is Winning in New Hampshire

Polls in the early states are notoriously poor predictors of the primary contests, and Sanders’ lead over Clinton is well with in the Quinnipiac Poll’s 3.4% margin of error.

But his rapid gain on Clinton in Iowa and New Hampshire reflects broader concern among liberal Democrats with economic inequality, college affordability, healthcare and campaign finance reform, issues that Sanders has trumpeted throughout his campaign.

“People are saying enough is enough,” Sanders said in an interview with TIME before the latest poll numbers were announced. “We are taking on the greed of the billionaire class. And they are very, very powerful and they’re going to fight back furiously. And the only way we succeed is when millions of people stand up and decide to engage.”

Clinton has sought to recalibrate her response to the email controversy, apologizing Tuesday for her use of a private email server and focusing on her economic message of raising middle class incomes while putting forth her own proposals for issues such as campaign finance reform.

Vice President Joe Biden, who is undecided about whether he’ll run for office again, placed a distant third at 12%, and former Maryland Gov. Martin O’Malley has support from just 3% of likely caucus-goers.

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