"The Sheriff sat in the bar parking lot and waiting for my friend to leave and start driving home before he stopped him. Isn't that entrapment?" The short answer is, "no."
Entrapment is a legal term that many have heard but few understand. The phrase is most often brought up in circumstances where citizens are questioning the appropriateness of law enforcement's actions or inaction. Entrapment does involve inappropriate conduct by law enforcement but it does not go as far as many people may initially believe.
Entrapment occurs when a law enforcement agent induces an individual to commit a criminal offense. In Iowa, the standard is whether law enforcement uses persuasion or other means that would be likely to cause normally law-abiding persons to commit the offense. Inducement is the key. If there is no inducement by a government agent, there is no entrapment. Merely giving an individual the opportunity to commit an offense does not amount to entrapment. Similarly, simply standing by and allowing an offense to be committed is not entrapment.
To use the example above. If an undercover law enforcement officer were to walk up to a drunk guy in the bar, beg him for a ride home, claiming that he needed to be with his dying mother in her last hours, only to have the Sheriff pull the guy over as he drives the devious officer to his "mothers" – that is entrapment. On the other hand, if the undercover officer simply sat in the corner counting the number of shots the guy took before the patron decided on his own to stagger out to his vehicle to drive home, only to be stopped by the Sheriff sitting in the parking lot – that would not be entrapment.
The point of the entrapment defense is that citizens should not be convicted of crimes that the government improperly persuades them to commit. The focus is on the conduct of the law enforcement agents because the general purpose behind the defense is to curb improper law enforcement techniques. If, however, a citizen commits a crime on their own accord, even if law enforcement is a witness (like many undercover drug transactions), the law can still hold the individual accountable and the defense of entrapment would not be available.