I have no idea on his current mental capabilities, but I want to remind everyone that is trying to diagnose him that he has a well documented and lifelong battle with a speech impediment. Stammering, stuttering, or mixing up words is more likely to be a sign of that condition than of dementia.

He's been way worse than he was in 2008.

Speech impediments can often take a substantial amount of effort and concentration to combat. They also aren't necessarily something that is overcome and then you are "fixed" and never have to think about again. They can often resurface when tired, stressed, drunk, or otherwise not at peak mental ability. The guy is obviously 12 years older than he was in 2008 and is likely more stressed and working harder as presidential nominee than he did as a nominee for VP. Like I said before, I don't know his mental capabilities and maybe there is some underlying problem there. However lots of the evidence I see can easily be attributed to that previously disclosed condition which by itself provides no indication of a lack of intelligence or coherence.

He seems to have trouble reading off a teleprompter and making a complete sentence. It seems intermittent.

Seems consistent with his speech impediment, no?

They don't. All of the "evidence" here is cherry-picked clips where Biden stumbles for 2 seconds within an hour-long speech. Even now, Biden's a far better speaker than all the people snidely passing these clips around.

We shall see about that in the debates.

He certainly does not appear capable of coherent thought or speech which is a little concerning given the job he is applying for.