Incumbent Presidents in the US almost always run for reelection to a second term, that's the normal expected outcome with vanishingly few exceptions in the last century.
The claim was Ds are more procedural than Rs. Asking what process the Ds followed to attempt to run, and then back out of running, biden (who again, was very obviously and publicly mentally incompetent) is clearly a rebuttal to a presented point.
You can repeat that as often as you want, but it doesn't seem well grounded. He's always had a stutter, and since he left office he has given speeches which suggest his mental faculties remain intact. Is he slowing down? Yeah. He's got quite a long ways to go before he's in McConnell territory.
In any case, what does his choosing to run have to do with process? Did he violate the process? Seems to me he was following it to a tee.
And all the shenanigans around 2016 when Bernie Sanders was shut out by the DNC. Even Elizabeth Warren said outright that the DNC rigged the 2016 nomination. I think the outcome would have been very, very different if the DNC didn't fuck with the timeline and forced Hillary as the Dem nominee.