I have read both
If you have read both, then you know that the Greeks had a cyclical view on the shifts between various forms of government.
When discussing democracy specifically, Aristotle identified the following factors as leading to their eventual replacement by tyranny or oligarchy:
1) Excessive equality - he recognized that equality was an overall desirable thing, but also understood the dangerous drawbacks of telling everybody that they are equal. When "equality" began to be applied to leadership and expertise, things would begin to fall apart.
2) Playground for demagogues - as Novichok pointed out, assh0les that promise people what they want to hear are often rewarded.
3) The rich and poor begin eating each other - with nobody acting as neutral arbiter between the haves and have nots, they rapidly begin to consume each other. One feels threatened by the idea of income redistribution, and the other feels butthurt through apparent lack of equity.
4) Gradual erosion of the rule of law - charismatic leaders with soaring personal ambition often override the rule of law, through promotion of nepotism and favoritism - at the expense of established institutions.
Once all these factors have a full chance to play out, the usual next step is either tyranny or oligarchy, according to Aristotle.
Can any of you recognize these symptoms in the modern United States?