Obama is basically irrelevant as a washed up puppet. But yes, the D’s need a far better candidate than anyone they’ve got now- if only to retain their power position in the House
As the old saying goes - you can’t beat somebody with nobody.
Donald J. Trump is the highest profile “somebody” out there, and the Democrats have not offered any substitute for that high profile.
I do not believe they could find anybody within their ranks that would measure up. Sure, Mike Bloomberg has more money and can provide sufficient backing for just about anybody, but he has the personal charm and charisma of a fence post.