Who could take President Biden's place?

Nearly twenty US Congressional Democrats have publicly urged President Joe Biden to step down from the presidential race, amid concerns that his faculties are declining with age. He has vowed to stay on despite making several blunders. Could Vice-President Kamala Harris replace Mr Biden as candidate if he steps down?

Also in the programme: UN peace talks to end Sudan's civil war fall through; and a new expedition seeks to explore the Titanic shipwreck.

(Photo: US Vice-President Kamala Harris campaigning in Greensboro, North Carolina. Credit: Lesser)