Important note: although I use references about the current President, my question should be regarded as a general one, not specifically related to Donald Trump.
According to this article Donald Trump disclosed a few details of one of his previous physical examinations:
Bornstein’s letter said Trump takes a statin to lower his cholesterol. So it is difficult to judge his cholesterol level of 169, his high-density lipoprotein level of 63 or his low-density lipoprotein level of 94. All are in the normal range. [...] Trump’s blood pressure of 116 over 70 was normal, as was his blood-sugar level, [...] liver function and thyroid function tests are all within the normal range [...]
But, nothing about any mental health examination.
According to this article, there seem to be a debate about Trump's mental health:
In a letter to the New York Times, 35 mental health professionals warned that the "grave emotional instability" indicated in Mr Trump's speech and actions made him "incapable of serving safely as president".
I am not interested in the actual details, only that there is a doubt coming from the some professionals about the mental health of the President. Of course, without proper professional evaluation, everything can be regarded as speculation.
On the theoretical level, according to this article, it is not impossible for one to suddenly develop mental illness, but this is typically linked to other condition. So, it can happen during a four-year term.
Most mental disorders develop slowly and get worse with time. Therefore, the sudden onset of a mental disorder is a red flag for biological abnormalities such as vascular disease, strokes, nutritional deficits, infections, hormone irregularities, tumors, or exposure to toxins.
This article informs about how can a President be impeached:
Well, the Constitution provides that the president can be impeached for treason, bribery, and what it calls other high crimes and misdemeanors.
The Constitution doesn't actually define what "other high crimes and misdemeanors" means. The historical sense is that it basically means, kind of, serious political crimes, sort of crimes against the state, crimes that involve abuse of office, abuse of power, abuse of trust.
So, nothing about mental illness.
I assume that mental health assessment is harder to be objectively performed, as opposed to physical one, which deals with clear intervals of normality, but I think that many aspects reached scientific consensus and can be used.
One example of such use is for mental evaluation of drivers, as indicated in this article (my emphasis on aspects that I find relevant for a possible evaluation of a President):
Mental Requirements
- Proper integration/interpretation of sensory input
- Focus of attention
- Proper associations of thought
- Appropriate judgment
Although driving a car (is done by one person) is very different from running a country (an entire staff exists), one could argue that running a country is by far more complex.
Question: is there a legal way that can be used to force the President of United States to undergo a mental health examination?
I think any reasonable person would consider that an official diagnosis can only be the outcome of a professional evaluation (not one based on what you see on TV, other media or short encounters)
I think you're wrong on that, and that this is why they made the Goldwater rule: because people implicitly trust "experts" even if their findings are based on nothing more than a mix of tv clips and political leanings.