Barack Obama reportedly expressed private doubts about Joe Biden becoming the Democrat presidential nominee in 2020.

According to Politico the former president told one Democrat: "Don't underestimate Joe's ability to f... things up."

Mr Obama was also said to have spoken about his own understanding of the 2020 Democrat electorate in Iowa.

"And you know who really doesn’t have it? Joe Biden," he reportedly said.

There were said to have been lingering tensions between the two after Mr Obama supported Hillary Clinton for the nomination in 2016.

Leon Panetta, Mr Obama’s defence secretary, told Politico: "He [Mr Biden] was loyal, I think, to Obama in every way in terms of defending and standing by him, even probably when he disagreed with what Obama was doing.

"To some extent, [he] oftentimes felt that that loyalty was not being rewarded.”

Some of Mr Obama's aides were said to have believed Mr Biden took discussions in the wrong direction when he was vice president.

In his book Ben Rhodes, Mr Obama’s former deputy national security adviser, wrote that "in the Situation Room, Biden could be something of an unguided missile”.

Mr Biden's aides were said to have believed his skills getting things achieved in Congress were under-appreciated.

Since Mr Biden secured the Democrat nomination Mr Obama has enthusiastically backed him and will be a keynote speaker at the Democrat Convention next week.