Trumpist media are leaning really heavily on this

Fox Follows Trump In Desperate Attack On Biden: 'Mentally Impaired'

They like to show clips of Joe B. refusing to take a cognitive test, though Trump took one.

Medical folks usually ask elderly folks or people subjected to heavy anesthesia who seem to be missing a few tricks too many to take these.

The point is to measure impairment that may or may not be long lasting, permanent, or worsening.