How to understand the Legality of What President Obama did in Amnesty

Remember the TV show Bait Car? A nice SUV put in a rough neighborhood to lure miscreants into stealing it, then lock it down, and arrest them to put them in jail.
The suckers always have a story.. "I thought it was my girlfriends car". It wouldn't be as interesting if they put the cars in the neighborhood with the keys in them, with the power to lock it down... and then when the thief steals the car, let them go, let them have the vehicle. That would be Prosecutorial discretion.

It's still illegal to steal a car. It's NOT illegal to let the guy go if you have that discretion. Eventually the cop that did this would be disciplined, perhaps eventually charged with incompetence. He did nothing wrong directly, just demonstrated incompetence. BUT having the discretion to let the thief go is indeed prosecutorial discretion. Within the constitution.
Andy of Mayberry might let a few guys go.. for a while. MERCY OVER JUSTICE. But eventually he would have been kicked out of office as sheriff if he kept it up. SO that's the deal. Now what?
Obama did an Andy of Mayberry thing.. it looked good on TV. Will the GOP do anything thing about this? Anything at all? CRICKETS... CHIRPING. This is a moot point. The bait car is gone. There is only one solution.. and it will never happen. Short of catastrophe we are stuck with Andy O and Joe Barney Biden till Jan 20, 2017. Just remember this in 2016, and then vote accordingly. This battle is lost, let's win the war.