Vermont senator Bernie Sanders has taken the lead from former secretary of state Hillary Clinton for the first time in a poll in the crucial early voting state of Iowa, as the self-declared socialist Democrat continues to tighten the race with the party establishment favorite.

A Quinnipiac University poll released on Thursday found that 41% of likely Democratic primary voters in Iowa said they would vote for Sanders, while 40% said they would vote for the former secretary of state. Though Sanders’ edge is within the margin of error of 3.4 percentage points, Clinton led Sanders by double digits in Iowa in July. Averages of all polling in the state show Clinton with a quickly eroding lead that nevertheless remains in the double-digits.

Recording an appearance on The Ellen DeGeneres Show on Tuesday, Hillary Clinton apologises over the email controversy. Guardian

The poll comes as Clinton continues to be dogged by the controversy over her use of a private email server, which she apologized for in an ABC interview this week after twice declining to do so. The release of the poll also comes amid ongoing deliberations over a potential run by Vice-President Joe Biden, who is said to be seriously considering a run against Clinton in the Democratic primary.

While Clinton remains on top in national polling and is still the party’s frontrunner, the surprising success of Sanders’ insurgent campaign has excited the Democratic primary the party once worried was going to be a coronation. Nonetheless, the shift is a marked one, recalling the 2008 Iowa race when Clinton, then the presumptive nominee, faltered and finished a disappointing third behind Barack Obama and John Edwards.



“[Sanders] is the candidate of the Democratic left, against his own party’s bosses and their prized presidential candidate, secretary Hillary Clinton,” said Peter Brown, assistant director of the Quinnipiac University poll.

The last Quinnipiac poll of the state, in July, found that 52% of voters said they would vote for Clinton compared with 33% for Sanders.



Other Democratic candidates, including former Maryland governor Martin O’Malley and former Virginia senator Jim Webb, have struggled to gain traction in polling so far. O’Malley gathered 3% and Webb failed to register above the mark while undeclared Biden came in third in the poll, with 12% of respondents saying they would vote for the vice-president.

The Quinnipiac poll also found that Sanders and Biden have a higher net favorability rating than Clinton and score higher ratings for honesty and empathy. A bright note for Clinton: more voters believe she has the leadership and temperament to handle an international crisis.

In the latest NBC News/Marist poll released on Sunday, Clinton led Sanders 48% to 37%. The poll also showed Sanders ahead 9% in New Hampshire, another crucial early voting state.