Biden can barely read the carefully prepared and crafted scripts entire teams develop for him – Biden certainly can not perform off script. This is typical and the best indicator of low intelligence or cognitively deficient people – they suffer when they go off script.
Obama performed his script reading very well; he rehearsed every speaking engagement. When he went off script, or free-form, he did OK, but not good. This is typical in politicians.
Politicians take multiple acting classes, receive advanced training in acting, body-language, and expressive speaking. Politicians are not real people when they are working – they are exactly the same as actors performing a scene, rehearsed from a script, until it appears believable.
Biden off script as we have seen at town halls, is a train wreck. He reverts to the his current level of intelligence, which is extremely diminished, and repeats catch phrases, insults, and references to questionable behavior.