Struggling to get his campaign back on track after its sudden diversion into the twilight zone of whether or not President Barack Obama was born in the United States, Mr Trump announced that, yes, indeed he was.

In the same breath he contended that the “birther” movement that had sought to cast doubt on the President’s place of birth had been started by Hillary Clinton and not by him at all.

He made the pronouncement in the clear hope that he could quickly dispense with an issue he once reveled in but which had, since Thursday, threatened to sow chaos in his campaign and potentially torpedo his nascent attempt to build bridges with black and minority voters.

“President Barack Obama was born in the United States, period,” Mr Trump said at a press conference at his newly opened hotel on Pennsylvania Avenue, blocks from the White House in Washington DC. “Now we all want to get back to making America strong and great again.”

It was, almost unbelievably, the first time that Mr Trump has formally disavowed the basic premise of the “birtherism” movement that he led earlier in this decade that held that Mr Obama had failed to demonstrate that he had actually been born in Hawaii.

It was a movement that clearly helped propel the conspiracy theories held by some on the alt-right flank of American politics that Mr Obama was somehow an imposter from another nation and – worse, in their contorted vision of the world – from a Muslim nation.

Since declaring his run for the presidency, Mr Trump has shied away from the topic, presumably aware that for great numbers of voters it had variously made him look foolish, if not racist and bigoted. But it burst back into the open on Thursday when he was asked outright to disavow it by The Washington Post in an interview and he demurred.

That led his own campaign to issue a statement later in the day insisting that Mr Trump did believe Mr Obama was born in Hawaii. It was in that statement that the campaign also for the first time made the astonishing claim, offering no evidence whatsoever, that it was Ms Clinton who had started the whole birtherism fandango when she was running against him in the 2008 primaries.

“Hillary Clinton’s campaign first raised this issue to smear then-candidate Barack Obama in her very nasty, failed 2008 campaign for President”, that statement, emailed to reporters, declared. “This type of vicious and conniving behavior is straight from the Clinton Playbook. As usual, however, Hillary Clinton was too weak to get an answer. Even the MSNBC show Morning Joe admits that it was Clinton’s henchmen who first raised this issue, not Donald J. Trump.”

Mr Trump made the same claim about Ms Clinton at his hotel on Friday. “I finished it. You know what I mean,” he added, a reference to the fact that in 2011 Mr Obama produced a long-form version of his birth certificate to put the whole issue to rest. Mr Trump has suggested that that only happened because of the pressure he had exerted and he had therefore done a service to the country.

Also in Washington DC on Friday, Ms Clinton lit into Mr Trump on the issue, demanding that he apologise to the country and to Mr Obama himself for having sown doubts about his birthplace.

Speaking to a group of black Democrat women, she said the whole Trump campaign had been “founded on this outrageous lie” and “there is no erasing it from history”. She added that Mr Trump is playing with the “worst impulses, the bigotry and bias” that lurks in the nation.

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“Think about how dangerous” it would be, she said, to have a leader in the Oval Office who “traffics in conspiracy theories and refuses to let them go no matter what the facts are”.

“Donald Trump is unfit to be present of the United States,” she said to loud applause. “We cannot become insensitive to what he says and what he stirs up. We cannot just accept this, we have got to stand up to it. If we don’t, it won’t stop.”

President Obama himself seemed to be conflicted between laughing at the latest Trump-led furore and denouncing it. “I am shocked that a question like that would come up when we have so much else to do,” he told reporters at the White House on Friday morning.

“Actually I am not that shocked,” he went on, not missing the opportunity to at least deliver a jab to Mr Trump. “I am petty confident about where I was born, I think most people were, as well.”