How to deal with doctors who, based on years of caring for a patient, do not do their professional duty to screen for cognitive decline?

Since 2015, I've given written permission, under POA, to do baseline test and it has not happened. Nurse says, oh yes, we will do so next time he comes in. When he comes in Dr. P says "John? He's fine, there's nothing wrong with him!" and doesn't do test. A year later I try again, now they get cagey and refuse to reply. This is a legal issue which is causing problems. A similar thing happened with a lawyer: he did a quick 2 minute cog. test and declared my Dad fine and shut me out of discussions, allowed my Dad to get in legal and financial distress, cause my Dad was afraid to fight a situation and just wanted it to go away. Of course, Dad is great at verbally fooling others and hiding his short term memory issues.

This has happened in WA state and I feel the Dr now has incentive to say, John is fine, so he doesn't have to take responsibility and liability for errors. He's 96 and no baseline cognitive tests have been done after going to same Dr for more than 18 years!