Former US presidential candidate John Kerry has cancelled plans to help other Democrats ahead of key polls next week, amid a row over remarks about troops.
On Monday he warned a group of students that if they neglected their education they might "get stuck in Iraq".
The comment drew criticism from the White House, which demanded an apology.
Mr Kerry said on Wednesday that his remarks were misinterpreted and that he personally apologised to any service member or American who was offended.
The Massachusetts senator's office said he had scrapped two campaign appearances so as not to become a distraction to Democratic candidates.
The statement added that Mr Kerry did not want to "allow the Republican hate machine to use Democratic candidates as their proxies in their distorted spin war".
In a second statement issued after prominent Democrats urged him to cancel public appearances, Mr Kerry said: "I sincerely regret that my words were misinterpreted to wrongly imply anything negative about those in uniform and I personally apologise to any service member, family member or American who was offended."
Mr Kerry had earlier said that he was sorry for a "botched joke" aimed at Mr Bush not US troops, and accused the administration of twisting his words.
The verbal gaffe comes just days ahead of US mid-term elections, which could hinge on the issue of the war in Iraq.
Mr Kerry, speaking to a group of California university students 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."
He added: "If you don't you get stuck in Iraq."
Mr Kerry's office said he had intended to say: "You end up getting us stuck in a war in Iraq. Just ask President Bush."
The BBC's James Coomarasamy, in Washington, says the White House seized on the comments to attack the decorated Vietnam War veteran and by extension his party.
On the campaign trail in Georgia on Tuesday, President George W Bush described the comments as "insulting and shameful".
"The members of the United States military are plenty smart and they are plenty brave and the senator from Massachusetts owes them an apology," Mr Bush said.
A White House spokeswoman said Mr Kerry's apology would probably draw a line under the affair.
"Senator Kerry's apology to the troops for his insulting comments came late but it was the right thing to do," Dana Perino told the Associated Press news agency.