In US politics, that mantle holds until someone else takes the nomination. That role is Biden's. It seems really odd that a former leader other than the most recent would be in charge of the party anywhere. (Remembering here that Biden is still alive and generally capable if suffering age-related decline. Also contextualizing with the fact that the sitting president is also obviously suffering age-related decline.)
> control of the party might pass to Michelle (like happened at least four times in Bangladesh, India, and Pakistan).
Yeah, I can see how someone from one of those countries might project onto US politics things that are not commonly done here. Relevant here is Obama beating Hillary for the nomination in 2008.
> After Biden’s disastrous debate in 2024, Obama was the one who swooped in to lead the party through the chaos
I am a political sicko, and I do not remember this happening. Are you perhaps elevating the importance of a single speech Obama gave?