Sure, there was the attempted assassination of Reagan and the fears for Obama as the first black President, but in those cases it was a lone nutter rather than a conspiracy.
How long can Trump crash the market before an angry billionaire decides to take him out? The remaining Koch brother is already pouring money into legal challenges against Trump…
He’s also useful. A lot of the kinds of people who might wish to be rid of him back in the day would much rather put him to use for their own ends.