For years, Trump was the most prominent proponent of the "birther" movement, which questioned whether US President Barack Obama had been born outside the United States and thus potentially constitutionally ineligible to be president - and calling on him to prove he was born in Hawaii.

As recently as Thursday he refused to answer a question from the "Washington Post" about his claim.

That ended this week when Trump and his campaign abruptly changed tack and conceded that Obama had indeed been born in Hawaii.

"President Barack Obama was born in the United States. Period," the Republican presidential candidate said at a press conference in Washington DC on Friday.

US Democratic Party presidential nominee Hillary Clinton's campaign called Trump's actions Friday "disgraceful."

"After five years of pushing a racist conspiracy theory into the mainstream, it was appalling to watch Trump appoint himself the judge of whether the President of the United States is American," Robby Mook said.

Earlier in the day, the Trump campaign issued a statement saying, "Having successfully obtained President Obama's birth certificate when others could not, Mr. Trump believes that President Obama was born in the United States."

Trump then pivoted and tried to blame his Democratic opponent, Hillary Clinton, for raising the issue and bragged that it was his pressure as a private citizen in 2011 that forced the president's hand in releasing his birth certificate.

Yet even if that were true, it fails to explain why Trump repeatedly made the claim for years to question the president's legitimacy in holding the country's highest office.

His comments speculating on Obama's birthplace have been seen by many as an attempt to delegitimize the nation's first black president, playing to a racist vein within American society but also losing votes from the non-white electorate.

Trump has been slowly chipping away at Clinton's narrow lead as the November race draws closer. The polling website realclearpolitics.com shows that Clinton's lead in an average of nationwide polls has slipped to 45.7 percent to Trump's 44.2 percent.

jar, dm/sms (AP, dpa)