If Trump really is falling into a deep mental decline, what are the legal implications of that?

[Silent3]

15. How often is anyone sent to a hospital trial without being declared guilty first in a courtroom?

While I believe Trump is truly a dangerous menace, with actual lives at risk if he regains power, he's not himself violently assaulting people, so I doubt he's the kind of person you can legally lock up in a prison, hospital prison or not, without first finding them guilty.

And if you aren't mentally competent to stand trial, I don't think you can be convicted of a crime. Can you be locked up until declared competent to hold you until trial? I don't know, but I suspect only when a trial for a violent crime is pending.

Besides, if Trump is losing it, it's almost certainly a one-way trip, not something that you could wait out until he's someone once again considered competent.