It’s also important for the physician to talk to someone who knows the patient well, because people who are slipping cognitively do not always recognize it. “Lack of awareness or insight can be part of the package” of dementia, said Dr. Ronald Petersen, director of the Alzheimer’s Disease Research Center at the Mayo Clinic in Rochester, Minn. (He emphasized that he was speaking in general terms, not specifically about President Trump’s case.)

If the doctor is concerned, and if a family member also says the subject is forgetful or repeating himself, and if this behavior is becoming a pattern — all those factors will influence the decision to “pursue this to the next level,” Dr. Petersen said.

Some patients simply prefer not to know if they are developing dementia. But those who do are given a neuropsychological test much more difficult and intense than the MOCA. And doctors will repeat it over time.

In such a test, for example, the examiner reads a short story and asks the subject to repeat it. Thirty minutes later, the subject is asked to repeat the story again.

The subject is also asked to draw geometric shapes and to remember them a half-hour later. The examiner may ask the subject to recall a list of 15 words as many as five times, and then recall them 30 minutes later.

What about Alzheimer’s?

The results of neuropsychological tests can tell doctors how a subject is performing relative to others of the same age, sex and education level. If the doctor thinks something is amiss, a clinical exam might follow to figure out what might be causing the problem.

Most cases of dementia result from Alzheimer’s disease. An M.R.I. scan can help with diagnosis. It can detect a stroke and other conditions. It also can determine if the hippocampus, the memory center of the brain, is shrinking, as happens in Alzheimer’s.