U.S. President Joe Biden on Friday said he did not need a cognitive test to determine whether he had a mental decline and dismissed calls from some Democrats that he should step aside to let a more vigorous candidate take on Republican Donald Trump.

However, Biden's performance in the 22-minute interview with ABC's George Stephanopoulos, widely billed as a crucial test of the octogenarian leader's fitness to run for a second term, was perceived a underwhelming. 

A defiant Biden, scrambling to defuse the political crisis over his shaky debate performance, argued that he had a bad night at the debate and that he was the right candidate to beat Donald Trump in the U.S. presidential race.

Under persistent questioning from Stephanopoulos, Biden dismissed polls showing him trailing Trump. Asked if he had undergone a specific cognitive test for a neurological exam, Biden, 81, said he had not had one and "no one said I had to."