I have another view on why the Obamas have been trotted out. Some people believe Moochelle may be drafted to run if Hillary continues to decline in the polls. Perhaps this is a trial run to see how the crowds react.
Possible, I suppose, but Michelle has absolutely no qualifications beyond being First Lady. At least Hillary argues she has experience as a Senator and Secretary of State. Asking people, even benighted Dems to vote for Michelle simply because she is a woman is a bit nervy.