Oh crap! You're right. After they run through Biden's half term and Harris's term and half they might select a person with severe down syndrome or severe autism to be our next president. Or perhaps because they have been using dead people's votes to get their candidates elected that next president might be actually dead.
But this is nothing new really. Woodrow Wilson became incompetent the last two years of his second term and his wife made all of his decisions for him, making her the first female president and the first (but not the last) unelected president.
Caption this Meme