Former U.S. President Barack Obama speaks as he campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

Former U.S. President Barack Obama speaks while visiting a canvassing location as he campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

Former U.S. President Barack Obama campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

Former U.S. President Barack Obama speaks next to a child while visiting a canvassing location as he campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

A Biden supporter wrapped in a U.S. flag wearing a late Justice Ruth Bader Ginsburg shirt looks on as former U.S. President Barack Obama campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

Former U.S. President Barack Obama speaks at a canvassing location as he campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

Former U.S. President Barack Obama speaks as he campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

With the skyline in the background, former U.S. President Barack Obama speaks at a drive-in campaign rally on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

Former U.S. President Barack Obama speaks as he campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

Supporters sitting on a car hold signs during a drive-in rally as former U.S. President Barack Obama campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

A supporter wearing a Kamala Harris face mask uses her mobile phone as former U.S. President Barack Obama campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

Former U.S. President Barack Obama campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

Former U.S. President Barack Obama takes questions as he campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

Former U.S. President Barack Obama waves after his speech as he campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.

Supporters watch at a drive-in rally as former U.S. President Barack Obama campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, U.S., October 21, 2020.