Hillary Clinton said on Saturday that she was "grossly generalistic" in calling half of Donald Trump's supporters a "basket of deplorables", after the Republican nominee argued that her comments had smeared many Americans and would take a political toll.
Less than 24 hours after she made the statement at a private New York City fundraiser Mrs Clinton said "I regret saying 'half' - that was wrong", But she argued that the word "deplorable" was reasonable to describe much of Mr Trump's campaign.
"He has built his campaign largely on prejudice and paranoia and given a national platform to hateful views and voices, including by retweeting fringe bigots with a few dozen followers and spreading their message to 11 million people," Mrs Clinton said.
Mrs Clinton, who has said she is the candidate to unify a divided country, made the "deplorables" comment at an LGBT fundraiser on Friday night at a New York City restaurant, with about 1,000 people in attendance.
"To just be grossly generalistic, you could put half of Trump's supporters into what I call the basket of deplorables. Right? The racist, sexist, homophobic, xenophobic, Islamophobic - you name it," she said, before stressing that other Trump supporters are frustrated and need sympathy.
Mr Trump and his supporters quickly pounced on the remark.
"Wow, Hillary Clinton was so insulting to my supporters, millions of amazing, hard-working people. I think it will cost her at the polls!" Mr Trump said in a tweet.
Running mate Mike Pence, in remarks at the Values Voter conference in Washington, shot back: "The truth of the matter is that the men and women who support Donald Trump's campaign are hard-working Americans, farmers, coal miners, teachers, veterans, members of our law enforcement community, members of every class of this country who know that we can make America great again."
The rhetorical scuffle comes as the candidates head into the final two months of the campaign, with Mr Trump trying to make up ground on Mrs Clinton before the November 8 election.
While Mrs Clinton is taking heat for her comment, Mr Trump's brand is controversy. At a rally in Pensacola, Florida, on Friday, he said Mrs Clinton is "so protected" that "she could walk into this arena right now and shoot somebody with 20,000 people watching, right smack in the middle of the heart. And she wouldn't be prosecuted".
The comment was reminiscent of Mr Trump's January description of the loyalty of his supporters.
"They say I have the most loyal people ... where I could stand in the middle of Fifth Avenue and shoot somebody and I wouldn't lose any voters, OK? It's like incredible," he said.
At the fundraiser, Mrs Clinton bemoaned the people she described as "deplorables", saying "unfortunately there are people like that. And he has lifted them up. He has given voice to their websites that used to only have 11,000 people - now how (many) 11 million.
"He tweets and retweets their offensive hateful mean-spirited rhetoric. Now, some of those folks - they are irredeemable, but thankfully they are not America," said the Democratic nominee, who was the country's top diplomat during President Barack Obama's first term.
Mrs Clinton then pivoted and tried to characterise the other half of Mr Trump's supporters, putting them in "that other basket" and saying they need understanding and empathy.
She described them as "people who feel that the government has let them down, the economy has let them down, nobody cares about them, nobody worries about what happens to their lives and their futures, and they're just desperate for change".
It could prove a stumble for a seasoned - and polarising - politician who wants to lead a country that includes many who have embraced Mr Trump's exhortations to "lock her up".
Mrs Clinton has made similar comments in the past. In an interview with Israeli TV this week, Mrs Clinton said that Trump supporters are, "what I call the deplorables; you know, the racists and the, you know, the haters, and the people who are drawn because they think somehow he's going to restore an America that no longer exists".
Clinton spokesman Nick Merrill said in a series of tweets after the remarks that Mrs Clinton has been talking about the "alternative right", or "alt-right" movement, which often is associated with efforts on the far right to preserve "white identity", oppose multiculturalism and defend "Western values".
Mr Merrill argued that "alt-right" leaders are supporting Mr Trump and "their supporters appear to make up half his crowd when you observe the tone of his events".
In her statement, Mrs Clinton said of Mr Trump: "it's deplorable that he's attacked a federal judge for his 'Mexican heritage', bullied a Gold Star family because of their Muslim faith, and promoted the lie that our first black president is not a true American. So I won't stop calling out bigotry and racist rhetoric in this campaign."
On Saturday, Mrs Clinton's staff said she attended another fundraiser at the Armonk, New York, home of attorney David Boies. But reporters travelling with her campaign were not allowed in and did not see her.
Comments about voters - especially at private fundraisers - have tripped up presidential hopefuls in the past.
Weeks before the 2012 election, Republican Mitt Romney landed in hot water for saying that 47% of the public would vote for President Barack Obama "no matter what" because they depended on government benefits and his job was "not to worry about those people".
During the 2008 Democratic primary, then-senator Obama said that small-town voters "cling to guns or religion or antipathy to people who aren't like them or anti-immigrant sentiment or anti-trade sentiment as a way to explain their frustrations".