[dragonwriter]

> I’d like to see a real world example of what you mean.

The German Enabling Act of 1933.

> when leaders are allowed to arbitrarily extend their reign past with their laws allow

What if they just use the provisions in the fundamental law that allow changing the structure or terms of government?

A state can either have a thanatocracy in which the dead dictate the details of government to the living, or it can have process by which even the fundamental law can be changed. If it has the latter, that process can, within the preexisting democratic system, be used to terminate democracy without anyone exceeding the power allowed in law.