Joe Biden is clearly showing worse signs of dementia. Democrats also had no problem with Harry Reid even though it was pretty clear he had pretty serious dementia towards the end of his term
Trump is actually the President of the United States, not a candidate or a former Senator. This is a person who can launch nuclear weapons if he thinks someone looked at him the wrong way or if his toast isn't prepared how he wants it. There is no whataboutism to be used here.
On top of that, Trump has clearly had mental and drug issues for years that can be compounded by dementia.
