Without knowing Obama's mind, only seeing his actions, how can you tell if he made the wise choice or the easy choice here?
How much weight does Barack Obama's endorsement actually carry, when he's just agreeing with what the voters have already decided for themselves?
Anyway, my point isn't that Obama's endorsement doesn't carry weight. It's that he has good reasons for preferring one candidate over the others, just like every other voter. And he can explain his reasons, just like any other voter. The argument that he shouldn't endorse Biden because then he'd have to explain why doesn't make much sense to me.
Presumably he's been able to make the case for nominating Biden for months, if not years. For whatever reason, he's chosen to hold off endorsing Biden until there's no need for him to make the case for it. Ironically, he's now just relying on the Obama image to boost voter enthusiasm for Biden in the general election. Which he could have done, and would have done, for whoever the presumptive nominee was. So his endorsement at this stage is pretty much a rubber-stamp.
Whether Obama's inner life includes a sincere and compelling case that has been made for Biden over the other candidates, we will probably never know.