Democrats were stampeding over one another yesterday to disassociate themselves from John Kerry, their presidential candidate two years ago, who has handed Republicans an election lifeline with remarks implying that US troops in Iraq are there because they are stupid.

Senator Kerry, speaking to a group of students in California on Monday, said: “You know, education, if you make the most of it, you study hard, you do your homework and you make an effort to be smart, you can do well. If you don’t, you get stuck in Iraq.” A video of his speech was placed swiftly on the internet and then seized upon by the White House, which has been desperate to switch the focus of voters away from the mounting toll in Iraq before Tuesday’s crucial elections for control of Congress.

On Tuesday night George Bush demanded that Mr Kerry apologise for his “insulting and shameful” remarks. Yesterday a number of top Democrat candidates joined him in calling on Mr Kerry to say sorry.

Harold Ford Jnr, who is running for the Senate in Tennessee, said: “Whatever the intent, [he] was wrong to say what he said.” Jon Tester, the party’s senatorial candidate in Montana, said: “He owes our troops and their families an apology.” Senator Hillary Clinton called the remarks inappropriate.

Democrat candidates across the US cancelled scheduled campaign appearances with Mr Kerry, whose distant hopes of another presidential candidacy in 2008 have now all but evaporated. Mr Kerry had insisted on Tuesday that it was Mr Bush who should apologise. But yesterday he said: “Of course I’m sorry about a botched joke. I mean, you know, it’s pretty stupid.” Later he issued an apology to the troops and their families.

He claimed that his remarks had been aimed at Mr Bush for being “intellectually lazy” in getting “us stuck in a war in Iraq” — but he had fluffed his lines.

Mr Kerry said that the mock-outrage of the White House was the latest example of the Republican campaign of “smear and fear” that had characterised attacks on his military record in Vietnam during the 2004 presidential contest, as well as his gaffe that he had voted for Iraq war funding before voting against it.

Dick Cheney, the Vice-President, twisted the knife yesterday with a direct reference to this when he told a campaign rally: “Of course, now Senator Kerry says he was just making a joke. I guess we didn’t get the nuance. He was for the joke before he was against it.”

Mr Kerry has previously attacked the so-called “chicken-hawks” who have cast aspersions on his military record, while never seeing combat themselves. Yesterday he made no reference to how Mr Bush had avoided service in Vietnam, perhaps because it would have meant conceding that the “intellectually lazy” President had got better grades than him at Yale.

• President Bush said last night that he wanted Dick Cheney and Donald Rumsfeld, the Defence Secretary, to remain in his Administration until the end of his term.

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