The Duty to Warn is not a list of occupations that are reportworthy. It's a high level "if there's a danger to self or the public" qualification. Politicians aren't special in that regard, and I think it's actually taken for granted within government operations that mentally ill politicians who are genuinely dangerous need to be identified and either treated or forced to resign.
There's actually some documentation of the increased formal White House psychiatric monitoring of Lyndon B. Johnson, as he was becoming unstable during the expansion of the Vietnam War. They were genuinely worried he'd crack and be useless in a domestic or defense crisis.
Duty to Warn legally protects the MD from confidentiality breach charges - arguably, that's the purpose of the legislation.
This site lists which US states have psychiatric mandatory/permissive Duty to Report legislation.
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MENTAL HEALTH PROFESSIONALS’ DUTY TO WARN]
Washington is a Mandatory Duty to Warn state, which means that not only is there no conflict with patient confidentiality, a psychiatrist who neglected this responsibility could be criminally liable.
DC is Permissive, which means in DC a psychiatrist is protected from privacy violations if they report a potentially dangerous diagnosed patient in good faith, but they don't
have to report.
Basically, what I was trying to clarify is that there's no "Catch-22" for the scenario where an actual in-person exam produces a diagnosis, the MD can report it to the appropriate authorities without concern of conflicting with patient confidentiality.