In what circumstances will a search warrant be used as a pretext for a search?

In Whren v. United States (1996) 517 U.S. 806, 116 S.Ct. 1769, 135 L.Ed.2d 89, police officers detained a motorist who they believed had committed a traffic violation. However, there was evidence the officers' subjective intent was to investigate illegal drug activity. During the detention, the police observed crack cocaine in plain view inside the vehicle. The high court rejected the defendants' argument that the traffic stop was a pretext, holding the officers' subjective intent would not invalidate a search that was otherwise justified under the circumstances viewed objectively. (Id. at p. 811, 517 U.S. at p. 1773, 135 L.Ed.2d at pp. 96-97.)