I've seen it a lot in older people's writing in different cultures before trump became relevant. It's either all caps or bold for some words in middle of sentence. Seems to be pronounced more in those who have aged less gracefully in terms of mental ability (not trying to make any implication, just my observation) but maybe it's just a generational thing.
I've seen this pattern ape'd by a lot of younger people in the Trumpzone, so maybe it has its origins in the older dementia patients, but it has been adopted as the tone and writing style of the authoritarian right.
That type of writing has been in the tabloid press in the U.K. for decades, especially the section that aims more at older people, and that currently (and for a good 15 years) skews heavily to the populist right.
Nah Trump has a very obvious cadence to his speech / writing patterns that has essentially become part of his brand, so much so that you can easily train LLM's to copy it.
It reads more like angry grandpa chain mail with a "healthy" dose of dementia than what you would typically associate with terminally online micro cultures you see on reddit/tiktok/4chan.
You can immediately identify them based on writing style and the use of CAPITALIZATION mid sentence as a form of emphasis.