Video: watch Hillary Clinton's remarks during an interview

Hillary Clinton rushed out an apology last night after citing the 1968 assassination of Robert F. Kennedy to defend her decision to remain in the race against Barack Obama — an insensitive blunder which caught her campaign aides off guard.

Mrs Clinton, dismissing the idea of abandoning her increasingly longshot attempt to win the Democratic presidential nomination, said in South Dakota: “My husband did not wrap up the nomination in 1992 until he won the California primary somewhere in the middle of June, right? We all remember Bobby Kennedy was assassinated in June in California. You know I just, I don’t understand it.”

She added that she did not understand why, given this history, some Democrats were calling for her to quit. The former First Lady had been responding to a question from a newspaper editorial board.

Mr Obama has been under Secret Service protection for more than a year after receiving death threats. Some within Mrs Clinton’s camp have talked in recent days about an “Act of God” strategy, but described it as the chance of the Illinois senator committing a serious blunder or being engulfed in a scandal that would render him unelectable.

For Mrs Clinton to mention the 1968 assassination in the context of this race was at the very least a clumsy way to justify her fading candidacy, and was immediately pounced upon by her rivals’ aides. Bill Burton, Mr Obama’s spokesman, said: “Senator Clinton’s statement before the Argus Leader editorial board was unfortunate and has no place in this campaign.”

James Clyburn, a senior African-American politician on Capitol Hill, who has criticised the Clinton campaign but remains an uncommitted superdelegate, said through a spokeswoman: “This is beyond the pale.”

Shortly after her remarks were publicised, Mrs Clinton rushed out a statement, through her campaign website, apologising for what she had said. “I regret that if my referencing that moment of trauma for our entire nation — and in particular the Kennedy family — was in any way offensive. I certainly had no intention of that whatsoever.” She added: “I was discussing the Democratic primary history and in the course of that discussion mentioned the campaigns of both my husband and Senator [Robert] Kennedy waged in California in June in 1992 and 1968 and I was referencing those to make the point that we have had nomination primary contests that go into June. That’s a historic fact.”

Robert Kennedy’s brother, Senator Edward Kennedy, who was found to have brain cancer this week, has endorsed Mr Obama. “The Kennedys have been much on my mind the last days because of Senator Kennedy,” she said.

Mrs Clinton’s comments came as Mr Obama faced growing calls to pick her as his running-mate, amid mounting concern inside the Democratic Party that he will struggle to win the White House without a “unity ticket”.

As Mr Obama began the vetting process formally this week, some senior Democrats, including Bill Clinton, had quietly begun a campaign to get Mrs Clinton back into the White House as vice-president. They argue that her victories in big battleground states such as Ohio and Pennsylvania, her ability to attract white, blue-collar households and women, and the more than 16 million votes cast for her candidacy, mean that Mr Obama must give her serious consideration.

Mr Obama is instinctively cool to the idea of having Mrs Clinton as his running-mate because it would run counter to his message of change. David Axelrod, his chief strategist, denied reports that discussions had begun between the two camps.

Mr Obama has many choices, including supporters of Mrs Clinton such as Ted Strickland, the Governor of Ohio, and Evan Bayh, the Indiana’s Senator. Several other women will be considered, including Janet Napolitano and Kathleen Sebelius, the Governors of Arizona and Kansas, and Senator Claire McCaskill of Missouri. He will also look at two other former rivals: Bill Richardson, the New Mexico Governor, and John Edwards.

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