What constitutes the crime of resisting an officer?

In California, the crime of resisting an officer is committed by "willfully resist[ing], delay[ing], or obstruct[ing] any public officer, peace officer, or an emergency medical technician . . . in the discharge or attempt to discharge any duty of his or her office or employment . . . ." (Pen. Code, 148, subd. (a)(1).) It is well established "'that when a statute makes it a crime to commit any act against a peace officer engaged in the performance of his or her duties, part of the corpus delicti of the offense is that the officer was acting lawfully at the time the offense was committed.' [Citations.]" (People v. Cruz (2008) 44 Cal.4th 636, 673; People v. Jenkins (2000) 22 Cal.4th 900, 1020 [discussing "the well-established rule that when a statute makes it a crime to commit any act against a peace officer engaged in the performance of his or her duties, part of the corpus delicti of the offense is that the officer was acting lawfully at the time the offense was committed"].)