US President Joe Biden has dropped out of the US presidential election and has endorsed Vice President Kamala Harris as the Democratic Party's new nominee - a massive political development with international ramifications. Mr Biden, who came under the scanner recently for his ability to lead the US given his age and mental fitness, has said that he was acting in the "best interest of my party and the country." He bowed out after a disastrous June debate against Donald Trump. Kamala Harris has confirmed her intention to become America's first woman president and to "defeat Donald Trump."