New Mexico AG says sheriffs must enforce gun control law

New Mexico's attorney general says law enforcement agencies must enforce a new law expanding background checks to nearly all private gun sales and that they could be liable for damage claims if they don't. Attorney General Hector Balderas issued the warning in a letter sent Thursday to police chiefs and county sheriffs, the Albuquerque Journal reported . The law will take effect July 1. Numerous county sheriffs opposed the legislation when it was being considered by the Democratic-led Legislature, but it was approved by lawmakers and then signed by Democratic Gov. Michelle Lujan Grisham on March 8. Balderas, a Democrat, told the law enforcement agencies that they have legal obligation to enforce the broadened background checks requirement regardless of whether they agree with the legislation. "As law enforcement officials," Balderas said, "we do not have the freedom to pick and choose which state laws we enforce." The president of the New Mexico Sheriffs' Association said Balderas' letter was premature because the law hasn't taken effect and because law enforcement officers have discretion in how they enforce laws. "We're elected by the people in our communities," Cibola County Sheriff Tony Mace said of his fellow sheriffs, "and that's what we're looking at - what do the people in our communities want?"...MORE

Law enforcement officers do have discretion in enforcing the law. As one Sheriff explained on his website

Oath of Office or Enforce all Laws

I have been asked why I would not enforce every present and future law as a Sheriff, essentially challenging that I should obey my oath and uphold all the laws created by local, state, or federal government without question. The Fort Wayne Journal Gazette had an editorial on May 1, 2013, chastising me for the premise that I would not enforce all laws.
Coming on the heels of a Second Amendment rally in South Bend, in which I participated in, the Journal writes, "We can't pick and choose which laws to follow and we can't allow selective enforcement of them, either...such selectivity breeds contempt for the law. A bad law should be struck down through the legislative process. A law of dubious constitutionality should be challenged in court. But while a law is on the books, it must be enforced. That applies to all of the laws all of the time. Someone who’s sworn duty is to uphold the law cannot be allowed to pick and choose which laws to enforce."
The South Bend Tribune printed an editorial on May 8, 2013, saying that I am a "public official sworn to uphold the law" and that I should not talk about "defying" a law. Both of these editorials, along with printed letters to area newspapers suggest that I am somehow breaking the law, and my oath, by defying a law.
Obviously law enforcement officers do not create laws. However, there is a misconception among some law enforcement officers and the public, that officers are just here to enforce the laws. In other words, there is a general expectation that we officers are supposed to check-our-mind-at-the-door and enforce any law regardless how unjust, oppressive or clearly unconstitutional a law is. This is not accurate.
The Journal Gazette and the South Bend Tribune mistakenly assume that my oath of office requires me to uphold all laws and that I have no discretion as to enforcement. The Sheriff's oath of office states, "I do swear or affirm to uphold and defend the United States Constitution and the Indiana Constitution, to the best of my ability, so help me God." This oath stems from Article VI, Section 3 of the United States Constitution, requiring all public servants to take this or similar oath. Nowhere in this oath does it require any law enforcement officer to enforce all laws.
This oath is meant to provide a checks and balance in our system of government. Our founding fathers knew there would be people who make mistakes, maybe even evil men, who would attempt to usurp the Constitution. When every public servant takes a solemn oath, then our Constitution has built-in safe guards at all levels, not just at the legislative and judicial levels.
In fact, the officers today have a great deal of discretion on enforcing laws. For example, officers enforce traffic laws daily. However, with high unemployment in the area, officers often give warnings, rather than a citation. In other words, an officer chooses not to enforce the law by not "arresting" someone. The action can still be beneficial to the community, by bringing attention to traffic safety. If all laws must be enforced without discretion, officers would never be able to give warnings and officers would not be able to make decisions that would divert persons from the criminal justice system. For example, an officer may choose to take a person home who was found in a state of public intoxication but not causing any trouble. There is no contempt of the law in either of these examples.
Would it not have been wonderful if there had been a constitutional officer present in December 1955, the day Rosa Parks was arrested, basically because of the color of her skin? The law was in place. However, the officer could have used his discretion. He could have offered her a ride home, praising her for her bravery for not giving up her seat, and essentially refusing to enforce an unjust and oppressive law.
Oath of office or blind enforcement? As for me, I will honor my Oath of Office.

And what about AG Balderas? Doesn't he have and exercise discretion? Of course he does, it is called prosecutorial discretion:

Prosecutorial discretion refers to the fact that under American law, government prosecuting attorneys have nearly absolute powers. A prosecuting attorney has power on various matters including those relating to choosing whether or not to bring criminal charges, deciding the nature of charges, plea bargaining and sentence recommendation. This discretion of the prosecuting attorney is called prosecutorial discretion.

 They both have discretion. If Balderas has and utilizes this discretion, why is he threatening law enforcement for exercising a similar discretion?