From “How Democracies Die”:
If authoritarians are to be kept out, they first have to be identi-fied. There is, alas, no foolproof advance warning system. Many authoritarians can be easily recognized before they come to power. They have a clear track record: Hitler led a failed putsch;
Chávez led a failed military uprising; Mussolin's Blackshirts engaged in paramilitary violence; and in Argentina in the mid-twentiet century, Juan Perón helped lead a successful coup two and a half years before running for president.
But politicians do not always reveal the full scale of their authoritarianism before reaching power. Some adhere to democratic norms early in their careers, only to abandon them later.
Then it goes on to explain how you can handle that harder second case. The funny thing is, we actually have the easier first case, and we still fucked up.