Before we get to that question, in your opinion:

What's the most unethical thing a public official can do?

Break campaign promises.

Waste, misappropriate, or steal public resources.

Buy or sell political favors.

Violate his or her oath of office (e.g., "to defend and uphold the Constitution").

Disagree with me.

Do I have to pick just one?

Consequeries | a series of queries about consequences.