Yep, it seems like a bizarre relic of a bygone era. This actually made me wonder if there's any place else in the government with this requirement. As far as I know, it only applies to the president. But what about the Vice President? He or she could be promoted if the president leaves. Then what about the Speaker of the House (3rd in line and I believe there is literally no requirement for the job; they're not even required to be a member of the house). I'm sure someone's thought through this already and there's a plan in place, but I never had.