Barack Obama and his wife Michelle have been slammed by his biographer for 'talking down' to voters in 'tone-deaf and clueless' preaching that harmed Kamala Harris' ill-fated presidential campaign.

The effect was so bad that – combined with Donald Trump's victory – it is likely to reduce the 44th president's political relevance to 'Bill Clinton levels', David Garrow said in an exclusive interview with DailyMail.com.

'People do not want to be talked down to, no matter who they are,' the 71-year-old Pulitzer Prize winner said.