1. Obama stumps for Biden in 2020 campaign trail debut

2. Former President Barack Obama waves while wearing a "Vote" mask as he campaigns on behalf of Democratic presidential nominee and his former Vice President Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

3. With the skyline in the background, Barack Obama speaks at a drive-in campaign rally on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

4. Supporters sitting on a car hold signs during a drive-in rally as Barack Obama campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

5. Barack Obama waves after his speech as he campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

6. A supporter wearing a Kamala Harris face mask uses her mobile phone as Barack Obama campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

7. A Biden supporter wrapped in a U.S. flag wearing a late Justice Ruth Bader Ginsburg shirt looks on as Barack Obama campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

8. Barack Obama campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

9. Barack Obama speaks next to a child while visiting a canvassing location as he campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

10. Barack Obama speaks at a canvassing location as he campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

11. Barack Obama speaks while visiting a canvassing location as he campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

12. Barack Obama campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

13. Supporters watch at a drive-in rally as Barack Obama campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

14. Barack Obama campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

15. Barack Obama campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

16. Barack Obama campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque

17. Barack Obama takes questions as he campaigns on behalf of Joe Biden in Philadelphia, Pennsylvania, October 21, 2020. REUTERS/Kevin Lamarque