A secretly filmed video has emerged showing Mitt Romney disparaging Barack Obama voters at a private donor dinner.
The Republican nominee is shown saying the 47% of Americans who back the president do not pay income tax and would never vote for Mr Romney.
"I'll never convince them they should take personal responsibility and care for their lives," Mr Romney says.
In a late-night appearance, Mr Romney said his remarks were not "elegantly stated", but did not retract them.
"This is the same message I give to people in public," he said in response to the video, released by liberal investigative magazine Mother Jones.
Earlier, his campaign said Mr Romney "wants to help all Americans struggling in the Obama economy".
"As the [former Massachusetts] governor has made clear all year, he is concerned about the growing number of people who are dependent on the federal government, including the record number of people who are on food stamps, nearly one in six Americans in poverty, and the 23 million Americans who are struggling to find work," spokeswoman Gail Gitcho said in a statement.
The Obama campaign was quick to pounce.
"It's hard to serve as president for all Americans when you've disdainfully written off half the nation," Jim Messina, Mr Obama's campaign manager, said in a statement.
The BBC's Adam Brookes in Washington says that this may prove to be a significant setback for Mr Romney, who has been relentlessly characterised by his political opponents as privileged and out of touch.
Also on Monday, Mr Romney's campaign unveiled a significant reworking of its strategy less than two months before election day.
Campaign advisers told the US media on Monday that Mr Romney would speak more on his specific policy proposals in the coming days and weeks.
Until now his message to voters has largely consisted of repeated attacks on President Obama's economic record.
'No matter what'
The video provided to Mother Jones is said to have been filmed at a private fund-raiser at some point after Mr Romney became the presumptive Republican nominee.
Its picture is blurred out with the exception of Mr Romney's face, and no attendees are visible.
The income tax segment is one of several clips posted online, in which Mr Romney expands at some length on his approach to the forthcoming election, and how his campaign will take on President Obama.
"There are 47% of the people who will vote for the president no matter what," Mr Romney is seen saying, referring to the percentage of Americans who have no income tax liability.
"There are 47% who are with him, who are dependent upon government, who believe that they are victims, who believe the government has a responsibility to care for them, who believe that they are entitled to health care, to food, to housing, to you-name-it. "
Mr Romney is later seen saying that his campaign has not been as harsh on Mr Obama as possible, because the president remains likeable and because of a desire to win the support of his otherwise disenchanted former supporters.
"Because they voted for him, they don't want to be told that they were wrong, that he's a bad guy, that he did bad things, that he's corrupt," he says, referring to independent voters who chose Mr Obama in 2008.
"Those people that we have to get, they want to believe they did the right thing, but he just wasn't up to the task."
Mr Romney also told the fundraising dinner he believes that if he won, there would be an immediate market-driven boost to the economy.
The videos bookended a difficult 24 hours for the Romney campaign. On Sunday, a lengthy Politico story detailed apparent divisions and indecision within the campaign.
That was followed by a public revising of campaign strategy on Monday morning.
"We are not rolling out new policy," campaign adviser Ed Gillespie said, "So much as we are making sure people understand that when we say we can do these things, here's how we are going to get them done and these are the specifics."
In that vein, the campaign released an online ad on Monday that discusses his economic plan. Advisers say the campaign will now speak more specifically about his budget plans and tax policy.
A series of opinion polls at the end of last week showed Mr Romney trailing Mr Obama both nationally and in several swing states.
The two men square off in the election on 6 November, but early voting begins soon in several states.