After US President Joe Biden’s shaky performance at the presidential debate on Thursday, many voters and Democrats have openly been questioning Biden’s ability to run the country.

According to reports, Democrats are thinking about replacing the 81-year-old president as the party’s representative for the US election which is to be held in November, The Guardian reported.

Although Biden and his campaign spokesperson have refuted any claims indicating his exit from the race, many are still wondering who the next candidate would be.

Vice President Kamala Harris would be the most obvious choice to replace Biden. She is the highest ranking female elected official in US history and the first Black and first Asian American to serve as vice president.

However, she too has suffered low approval ratings. Nearly 50% of voters have an unfavourable view of her, according to 538 polling average.

Other possible contenders are Michigan governor Gretchen Whitmer, Illinois governor JB Pritzker, California governor Gavin Newsom and Maryland governor Wes Moore.

Biden’s age and mental acuity has long been a hot topic in the electoral campaign. After his performance in the debate on Thursday, even his staunchest supporters have stumbled.

Republican candidate Donald Trump challenged the president to take a cognitive test. He said, "I don’t know what he said at the end of that sentence. I don’t think he knows what he said either."