One of the requirements to become President of the United States is that you must be at least 35 years old, but there is no upper limit to how old someone can be as President. As people age, their cognitive abilities decline. Go watch a Donald Trump interview from the 90s then watch an interview from last year. Ignoring politics or my opinion of him, there is a very clear difference in how he speaks. When he entered office, Trump was 70 years old and was the oldest anyone has ever been at the beginning of their Presidential term. If elected, Biden would be 78 years old. There’s no reason for a nearly 80 year old man to hold one of the most powerful elected positions in the world. Being President of the United States is too stressful of a job for someone that old.
The video in linked shows Biden struggling to recite the opening of the Declaration of Independence. The argument could be made that it was just a simple mistake, everyone stumbles over their words once in a while. But these clips are becoming more and more frequent. What’s the saying, where there’s smoke there’s fire? If Biden can barely recite something he should know by heart after a lifetime in politics, imagine what else he can barely do.