Can a defendant rely on the reasonableness defense in a civil case?

Even if the violated right was clearly established at the time of the violation, it may be "difficult for [the defendant] to determine how the relevant legal doctrine . . . will apply to the factual situation the [defendant] confronts ... . [Therefore, i]f the [defendant's] mistake as to what the law requires is reasonable ... the [defendant] is entitled to the immunity defense." Saucier, 533 U.S. at 205. The reasonableness inquiry is objective: "the question is whether the officers' actions are 'objectively reasonable' in light of the facts and circumstances confronting them, without regard to their underlying intent or motivation." Graham v. Connor, 490 U.S. 386, 397 (1989).