Kamala Harris 'obvious candidate to replace' Biden should he bow out

US President Joe Biden returns to the campaign trail Friday, pushing ahead with his reelection bid after a mixed performance at a major news conference failed to silence calls for him to quit. The 81-year-old will give a speech bashing rival Donald Trump in Detroit in the rust-belt state of Michigan, a crucial battleground state that the Democrat must win in November's election. A defiant Biden insisted in a pivotal appearance at a NATO summit on Thursday that he would run again, and win -- despite concerns about his age and health following a disastrous debate performance two weeks ago. But a series of gaffes, including referring to Vice President Kamala Harris as "Vice President Trump," kept Biden's fitness for a second term under the microscope. The top Democrat in the House of Representatives Hakeem Jeffries just met with Biden. As the number of members calling on the president to step aside rose to 20, FRANCE 24 is joined by Dr Richard Johnson, Senior Lecturer in US Politics & Policy at Queen Mary University of London.