Bernie Sanders is beating Hillary Clinton in a nationwide opinion poll of likely Democratic primary voters for the first time.
The Fox News survey has Mr Sanders on 47 per cent among likely voters and Ms Clinton trailing three points behind on 44 per cent.
The independent socialist senator from Vermont is up from ten points from 37 per cent in January while the former First Lady and Secretary of State is down five points from 49 per cent a month ago.
The poll is by definition an outlier – but suggests a closing gap between the two candidates in the race.
Ms Clinton’s overall lead in news network CNN’s polling average has narrowed to just six points.
Mr Sanders, a self-described democratic socialist, has ridden a wave of support from young and low income people to run the Demoratic establishment candidate favourite close.
He has run on a platform of increasing the minimum wage, making education free and accessible to all, and taking on the political and economic establishment.
His rival has responded with a marked shift of rhetoric and policy in a more left-wing direction.
Mr Sanders has been bolstered in recent months by well-received debate performances and a highly efficient grassroots fundraising model built on small donations.
He has accused his rival of being beholden to interests on Wall Street and the political establishment, calling for a “political and economic revolution”.
Ms Clinton has however accused Mr Sanders of lacking foreign policy experience.
The Vermont senator last week released a viral video advert in an attempt to attract the support of ethnic minority voters, who he had previously been weak amongst.
Match-up polling against likely Republican candidates for the presidency shows Mr Sanders performing better overall that Ms Clinton, largely because Ms Clinton has higher negative ratings.
Mr Sanders overwhelmingly won the New Hampshire primary, the second contest to determine the nomination, and effectively tied with Ms Clinton in the Iowa Caucuses, the first round of voting.
Ms Clinton however has already massed a large number of delegates to vote for her at the nominating convention on account of having stronger connections with the Democratic Party establishment.
The winner of the Democratic primary will go to face the Republican nominee in the presidential election in November. Business Donald Trump is currently the frontrunner to win that nomination.
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