During one of the US presidential debates in September last year, Donald Trump for the first time publicly acknowledged that Barack Obama was born in the US. In fact, he blamed his opponent Hillary Clinton for starting the “birther” conspiracy, a statement that has been disproven by numerous fact checkers.

Privately, however, Trump apparently remains unconvinced that the birth certificate of the former president is authentic. That tidbit was reported in a New York Times article (paywall) published yesterday (Nov. 28), which details how Trump has continually changed his story on a number of issues, most notably on whether he was the voice on the Access Hollywood recordings making lewd comments about sexually assaulting women. The release of the 2005 tape nearly derailed his campaign, forcing Trump into damage control and to apologize for the remarks.

The Times story cites unnamed advisors, including a senator, who say Trump has brought up the conspiracy around Obama’s birth certificate in closed-door conversations. Rumors around Obama’s birth certificate had circulated for a while, but Trump arguably pushed the birther movement to the mainstream.

In 2011, the White House released a copy of Obama’s original long-form birth certificate, which Trump happily took credit for. It’s not clear how much more proof he needs.