But he also stepped up attacks against his Democratic rival Hillary Clinton, accusing her of initiating the doubts about Obama and later raising the spectre of violence against her again.
In a much-hyped televised event, Trump gave a lengthy plug for his new Washington hotel before acknowledging that “President Barack Obama was born in the United States, period.”
The mogul-turned-politico pointedly did not apologise, nor did he walk back similarly baseless claims that Obama – whose father was a Kenyan Muslim – founded the violent Islamic State group.
Instead, he tried to pin blame for “birtherism” on his Democratic rival Hillary Clinton, whom he accused, without evidence, of starting the movement that questions Obama’s nationality and right to be president.
“Her campaign of 2008 started the birther controversy. I finished it. I finished it. You know what I mean,” Trump said.
The celebrity TV star has questioned Obama’s US citizenship – a legal prerequisite for becoming president – since at least 2011.
The White House has long viewed Trump’s claims as a racist attempt to delegitimize the president.
The charges also served to launch Trump’s political career, propelling him onto the national stage and winning him fans on the far right.
But five years on, now in a tight presidential election race, Trump’s position has become a liability, repulsing black, Hispanic and moderate voters whose support he needs to win the Oval Office.
The controversy reignited Thursday when Trump again demurred on Obama’s citizenship, forcing his campaign into damage control.
Threat of violence
Trump’s Democratic rival Hillary Clinton jumped on the statement as more evidence that Trump is unfit to be president.
“For five years, he has led the birther movement to delegitimize our first black president,” she said. “His campaign was founded on this outrageous lie. There is no erasing it in history.”
“He’s feeding into the worst impulses, the bigotry and bias that lurks in our country,” she added.
Trump went on the attack again later in the day at a Miami rally, where he entered as the epic theme from the musical “Les Miserables” rang out, a reference to Clinton’s recent remarks in which she called “half” of Trump backers “deplorable.”
At the Florida event the bombastic billionaire suggested Clinton’s Secret Service guards voluntarily disarm and “see what happens to her.”
Members of Clinton’s government-appointed guard detail should abandon their weapons because she wants to “destroy your Second Amendment,” he said, referring to the US Constitution’s clause that enshrines the rights of Americans to bear arms.
“I think that her bodyguards should drop all weapons,” the real estate billionaire told a cheering rally. “Take their guns away. She doesn’t want guns. Take them. Let’s see what happens to her…It will be very dangerous.”
Clinton campaign manager Robby Mook condemned Trump’s remarks, saying they “should be out of bounds for a presidential candidate.”
CNN and other major TV stations did not broadcast Trump’s rally as they often do, suggesting the US media is heeding widespread criticism that it devotes too much attention to the Republican candidate.
Bigotry and bias
First Lady Michelle Obama also criticised Trump during her 2016 campaign debut Friday, saying the choice for voters is “excruciatingly clear” between Clinton and a candidate who “traffics in prejudice, fear and lies.”
She said her husband had answered slanders through legislative achievements and “by going high when they go low,” as she encouraged supporters to go to the polls.
The latest opinion surveys indicate a tight race, although Clinton retains a notable lead in vital battleground states.
Asked in the Oval Office about the renewed birther controversy Friday, President Obama gave the question short shrift, making a dig at the US media and its obsessive coverage of Trump.
“I am shocked that a question like that would come up at a time when we have so many other things to do,” he said, before adding: “Well, I am not that shocked.”
“I was pretty confident about where I was born. My hope would be that the presidential election reflects more serious issues than that.”
Obama produced his birth certificate in 2011 – showing he was born at the Kapiolani Medical Center in Hawaii on August 4, 1961 – to put an end to the allegations.
Appearing at the White House Correspondents’ Dinner shortly after, he publicly ridiculed Trump, who was in the audience.
“No one is prouder to put this birth certificate matter to rest than The Donald,” Obama said.
“And that’s because he can finally get back to focusing on the issues that matter, like, did we fake the moon landing? What really happened in Roswell? And where are Biggie and Tupac?”