US Democratic presidential candidate Hillary Clinton faced a firestorm Saturday sparked by her raising the 1968 assassination of Senator Robert Kennedy to justify her decision to prolong her White House campaign. Clinton told a newspaper board in South Dakota she could not understand calls for her to quit, arguing that history showed that some past nominating contests had gone on into June. “My husband (Bill Clinton) did not wrap up the nomination in 1992 until he won the California primary, somewhere in the middle of June, right?” Clinton said Friday in an interview with the Argus Leader newspaper editorial board. “We all remember, Bobby Kennedy was assassinated in June in California, I don't understand it,” Clinton said while referring to calls for her to pull out of the Democratic race in which the final nominating primaries are held on June 3 in South Dakota and Montana. Clinton, who later expressed regret over the remark, made it to the editorial board of a South Dakota newspaper, the Sioux Falls Argus Leader, when explaining that other races for the Democratic presidential nomination had lasted into June. Clinton launched the damage control effort, saying that the Kennedys had been in her thoughts, after Senator Edward Kennedy was diagnosed with brain cancer this week. “I regret that if my referencing that moment of trauma for our entire nation, and particularly for the Kennedy family, was in any way offensive. I certainly had no intention of that, whatsoever,” the former first lady said. The Democratic nominee will face Republican John McCain in the November election. A spokesman said Clinton had simply been pointing out that Democratic campaigns in the past had continued into June and therefore people should not be pressuring her to withdraw. “She was simply referencing her husband in 1992 and Robert Kennedy in 1968 as historical examples of the nominating process going well into the summer. Any other reading is inaccurate,” Clinton spokesman Mo Elleithee said. Clinton's comments drew a sharp response from the Obama campaign. “Senator Clinton's statement before the Argus Leader editorial board was unfortunate and has no place in this campaign,” said Obama campaign spokesman Bill Burton. He condemned her comment as “unfortunate” and said it “has no place in this campaign.” Referring to political assassinations is fraught with sensitivity, especially for supporters of Obama, who accepted Secret Service protection last year, long before the time it is offered to most presidential candidates, because of unspecified threats. Kennedy, brother of slain US president John F. Kennedy and Massachusetts Sen. Edward Kennedy, was assassinated during his 1968 race for the Democratic presidential nomination. Robert Kennedy Jr., son of the slain senator, said in a statement, “It is clear from the context that Hillary was invoking a familiar political circumstance in order to support her decision to stay in the race through June.” “I understand how highly charged the atmosphere is, but I think it is a mistake for people to take offense,” said Kennedy, a Clinton supporter unlike some other members of his family, including Sen. Edward Kennedy, who back Obama.