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…
Something that will really perk up my attention is if people start shooting at his security. That will indicate anger is so ripe that even protecting him makes you a target.