Barack Obama has not yet endorsed Kamala Harris' presidential bid because he is skeptical about her ability to beat Donald Trump, a Biden family insider has claimed.

Harris won the backing of a majority of the Democratic Party delegates on Monday, a day after President Joe Biden, 81, announced that he was dropping his reelection bid and, shortly after, endorsed the Vice President.

Top Democrats, including Nancy Pelosi and Gavin Newsom, quickly rallied behind Harris, 59, and issued public support of her campaign - but Obama has remained noticeably silent.

A source close to Biden's family told the New York Post that the former president is 'very upset' about Harris' candidacy, even claiming that he 'knows she can't win' against Trump, 78. 

The insider further went on to claim that Obama, 69, believes Harris is 'incompetent' and 'cannot navigate the landmines that are ahead of her'. 

But other Democrats told Dailymail.com Obama has privately fully supported Harris' candidacy and has been in regular contact with her throughout this week. 

They claim he believes her campaign is going well and he's set to publicly endorse her soon. 

NBC, meanwhile, is reporting aides for Harris and Obama have 'discussed arranging for the two of them to appear together on the campaign trail'.