Barack Obama’s foreign policy adviser resigned yesterday after describing Hillary Clinton as a “monster” who would do anything to win.

The departure of Samantha Power for insulting remarks made to The Scotsman newspaper during a visit to London reflects how the Democratic presidential race has been transformed in the past five days.

After weeks in which Mr Obama had shrugged off Mrs Clinton’s flailing attacks, he is now the candidate who appears most rattled with his campaign promising to go negative itself – and making mistakes.

Earlier this week Mr Obama fled a press conference asking him awkward questions about his relationship with former fundraiser, Tony Rezko.

David Axelrod, Mr Obama’s strategist, later responded by threatening to dredge up material about Mrs Clinton’s past – including the Whitewater scandal – but her campaign was swift to compare him to Ken Starr, the notorious investigator who hounded the White House in the 1990s.

Ms Power’s resignation today came after Mrs Clinton’s campaign had successfully capitalised on her remarks by contrasting it with Mr Obama’s high-moved rhetoric.

Ms Power made the offending remark during a trip to London this week in which she was apparently too candid about the problems facing the Obama campaign.

"We f***** up in Ohio," she told the newspaper. "In Ohio, they are obsessed and Hillary is going to town on it, because she knows Ohio's the only place they can win.

"She is a monster, too – that is off the record – she is stooping to anything," Ms Power added. The newspaper described her as "hastily trying to withdraw her remark".

Scotsman editor Mike Gilson tonight stepped in to defend his use of the "off-the-record" quotes.

He said: "We have no opinion on whether Ms Power was right to quit and perhaps politics should be able to retain people with talent who are prepared to learn by their mistakes but we are certain it was right to publish. I do not know of a case when anyone has been able to withdraw on the record quotes after they have been made.

"The interview our political correspondent Gerri Peev conducted with Ms Power was clearly on an on-the-record basis. She was clearly passionate and angry with the tactics of the Clinton camp over the Ohio primary and that spilled over in the interview. Our job was to put that interview before the public as a matter of public interest. It was for others to judge whether the remarks were ill-judged or spoke of the inexperience in the Obama camp."

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