WASHINGTON - For the first time since declaring his presidential run, Republican Donald Trump acknowledged that his caustic comments may have caused people pain, saying that he regrets some of what he's said "in the heat of debate" as the billionaire businessman and his revamped campaign staff look to recover from a rough few weeks.

A day after announcing a campaign shake-up and as he trails in the polls, the Republican presidential nominee said that he recognized that his comments - which have angered minorities and alienated large swaths of the general election electorate - may have been ill-advised. “As you know, I am not a politician. I have worked in business, creating jobs and rebuilding neighborhoods my entire adult life. I’ve never wanted to learn the language of the insiders, and I’ve never been politically correct - it takes far too much time, and can often make it more difficult to achieve total victory,” Trump said at a rally in Charlotte, North Carolina.

“Sometimes, in the heat of the debate and speaking on a multitude of issues, you don’t choose the right words or you say the wrong thing. I have done that, and I regret it, particularly where it may have caused personal pain. Too much is at stake for us to be consumed with these issues." The speech comes just days after Trump reshuffled his campaign leadership, naming pollster and former adviser Kellyanne Conway as campaign manager and Breitbart executive Steve Bannon campaign CEO, an ultra-conservative.

His expression of regret may come as a surprise to those who expected Bannon to reject any efforts by other advisers to polish Trump's message in the home stretch of the general election. Conway said she didn't want Trump to lose his "authenticity."

Paul Manafort resigned as chairman of U.S. Republican candidate Donald Trump's presidential campaign on Friday, days after he was effectively demoted in a shake-up of the campaign's leadership. "This morning Paul Manafort offered, and I accepted, his resignation from the campaign," Trump said in a statement.

"I am very appreciative for his great work in helping to get us where we are today, and in particular his work guiding us through the delegate and convention process. Paul is a true professional and I wish him the greatest success," Trump said.

A spokeswoman for the campaign of Donald Trump, the Republican presidential nominee, has said that his Democratic rival Hillary Clinton suffers from a rare language disorder caused by brain damage, a claim Clinton’s doctor quickly denied as false.

Katrina Pierson, who is not a doctor, issued her diagnosis on MSNBC-TV, saying Clinton suffers from dysphasia, a disorder caused by brain disease or damage.

“What’s new are the other reports of the observations of Hillary Clinton’s behaviour and mannerisms ... as well as her dysphasia, the fact that she’s fallen, she has had a concussion,” Pierson said Thursday.

Trump, who has been accused of offending Mexicans, Muslims, immigrants, the disabled and fellow Republicans such as John McCain during his 14-month presidential campaign did not specify which comments he regretted and said at one point that journalists have often taken him "out of context." Throughout the campaign, Trump has generally refused to apologize for remarks viewed as insensitive or insulting.

The Republican nominee also said that "too much is at stake for us to be consumed with these issues," little more than 80 days before the election against Democratic opponent Hillary Clinton, one in which he currently trails according to numerous polls. Critics expressed skepticism over Trump's contrition.

Clinton campaign spokesperson Christina Reynolds said Trump "literally started his campaign by insulting people," and his "apology tonight is simply a well-written phrase until he tells us which of his many offensive, bullying and divisive comments he regrets - and changes his tune altogether.”

Trump told supporters in Charlotte he would "speak the truth" on behalf of Americans who have lost jobs and been failed by government run by "insiders" who only look out for themselves.

The trip to North Carolina - a key state in the Nov. 8 national election - came a day after Trump announced major changes to his campaign staff. Stephen Bannon, the executive chairman for Breitbart News, is the new campaign CEO, while pollster and consultant Kellyanne Conway is campaign manager. Paul Manafort, the aide who had wielded the most control, remains as campaign chairman.

In another sign of a changed approach, Trump delivered a speech at the Charlotte Convention Center with a teleprompter, the third time this week he has read from a prepared text.

In previous weeks, Trump has read prepared remarks at smaller events devoted to economic and foreign policy, including a Monday address in Ohio on fighting terrorism.

During an event Tuesday near Milwaukee, Trump spoke about the need for "law and order" and to challenge what he described as a corrupt political establishment, themes he also hit during his speech in Charlotte.

He also made an appeal for African-American voters - as he did in Wisconsin - saying no community should be "left behind" and that Democrats have failed them for decades.

Democrats and some Republicans have criticized Trump's hiring of Bannon, whose Breitbart news site is known for its aggressive support of Trump and condemnation of Clinton as well as the Republican establishment. Aides to Clinton said the Bannon hire signals a raft of attacks and conspiracy theories will be emanating from the Trump camp over the next two-and-a-half months.

“After several failed attempts to pivot into a more serious campaign, Donald Trump has decided to double down on his most small, nasty and divisive instincts,” Clinton campaign manager Robby Mook said.