How did the Roman Republic become a dictatorship?

General Sulla was declared leader after a long civil war.
The patricians and senators were defeated by General Sulla.
General Sulla challenged and defeated his opponent in an election.
The plebeians supported General Sulla’s overthrow of the government.

General Sulla was declared leader after a long civil war.

Explanation:

Civil War:

Marius led an army for the plebians.

vs.

Sulla led an army for the patricians and senators.

then...

Sulla won and was dictator.

four sitting presidents have been assassinated while in office but the first was abraham lincoln,

social contract theory, nearly as old as philosophy itself, is the view that persons' moral and/or political obligations are dependent upon a contract or agreement among them to form the society in which they live