"It may be the most important and widely anticipated presidential debate in the United States of all time. The election is razor thin," US political analyst and Director of Debate at University of Michigan Aaron Kall tells AFP during an interview, as Joe Biden and Donald Trump prepare for the biggest moment so far in the US election -- the first of two high-stakes debates that could upend the race. "If President Biden makes a disqualifying gaffe, he could literally end his hopes for reelection," Kall explains, adding that Trump rambling over who won the 2020 election "could offend moderate independent voters, which he needs to to win the election." SOUNDBITES