US President Donald Trump on Monday taunted opponent Joe Biden for forgetting his name and calling him "George". Biden's habit of verbal gaffes reemerged on Sunday evening when he struggled to remember Trump's name as he addressed a virtual concert by TV link. "Four more years of George, er, George, er, he -- we're going to find ourselves in a position where, if Trump gets elected, we're going to be in a different world," Biden said. Trump has sought to paint Biden as mentally unfit for office, and the president swiftly jumped on the moment of forgetfulness. "Joe Biden called me George yesterday. Couldn't remember my name," Trump tweeted with glee. "The Fake News Cartel is working overtime to cover it up!"