USA - can police be criminally charged with false imprisonment for a retaliatory arrest?

Question

For example, say a police officer arrests someone for giving them the finger. As I understand it this action is protected under the first amendment.

Can any criminal charges be brought against an officer that does this?

Answer 1

Yes.

Examples of officers charged with false imprisonment for making an arrest without a valid legal basis to do so can be found here, here, and here (the exact name of the criminal offense varies somewhat between the federal criminal justice system and the various respective state criminal justice systems).

In general, police do not have immunity from criminal charges if they can be proven, and the legal protection that law enforcement officers enjoy when making an arrest apply only to arrests that was lawful or that a law enforcement officer reasonably believed was lawful.

As a practical matter, it is rare for police officers to be charged with false imprisonment criminally, and much more common for a civil lawsuit under 42 U.S.C. § 1983 to be brought against an officer by the victim of the wrongful arrest (see, e.g., here).

But no legal doctrine prohibits the criminal charge if the officer knew that the arrest was unlawful.