Any populist movement, which manages to gain power in a country, must transition the political system into an autocratic state or it will sooner or later be defeated in an election. This fact makes populist movements that more dangerous and unpredictable.

Another mechanism being - the more successful a populist movement is in gradually capturing the institutions of the state, the riskier it becomes for the same movement to lose power, because of the threat of legal action against its leaders that might ensue.

Populist movements which come and go, usually in one electoral cycle, are the least dangerous. Those that manage to prolong the duration of their authority over two or more electoral cycles become more and more unhinged as their power gets rooted.

This isn't a psychological statement about individuals being corrupted by power, it is a structuralist argument that successful populist leaders build illegal networks, tying various non-state actors together (such as the blending of organized crime with security agencies).

They do this not only to gain personal wealth, but to assert control, which drastically lowers the chances of mainstream opposition getting the country back on track. Capturing of the state, illegal actions included, is necessary for the survival of the populist movement.