Kamala Harris secures endorsement of former speaker Nancy Pelosi

Vice president Kamala Harris speaks from the South Lawn of the White House (Susan Walsh/AP)

Vice president Kamala Harris has moved swiftly to lock up Democratic delegates behind her campaign for the White House after President Joe Biden stepped aside amid concerns he would be unable to defeat Republican Donald Trump.

Mr Biden’s exit on Sunday, prompted by Democratic worries over his fitness for office, was a seismic shift to the presidential contest that upended both major political parties’ carefully honed plans for the 2024 race.