WASHINGTON (AP) – Former President Barack Obama is returning to Philadelphia for his first in-person 2020 campaign event for Joe Biden. He’ll be speaking Wednesday at a drive-in rally, where supporters will listen to him over the radio inside their cars. The format underscores the challenge Democrats face in ginning up enthusiasm and getting out the vote in a year when they’ve eschewed big rallies in favor of small, socially distanced events. But Democrats say Obama remains one of the party’s greatest assets in the final stretch. Obama has already been helpful to the Biden campaign. He’s appeared at virtual fundraisers and encouraged young Americans to vote.