“The List.” Almost everyone is in favor of background checks, with polls showing anywhere from 85 percent to 95 percent of respondents saying would-be gun purchasers should undergo a background check before they can walk out of a store packing heat. But a check against what? Did the person commit a crime? Or is the seller checking to find out whether the buyer at one point sought medical treatment for substance abuse or has been accused of stalking by a former (perhaps crazy) spouse? Who gets included on “the list” of people who can’t own a gun? …

Defining Mental Illness. FBI guidelines on mental illness have yet to be updated and still refer to an “adjudicated mental defective” as a person who should be denied a gun purchase. The definitions of mental “defectiveness” are relatively narrow—involuntary commitment to a mental institution or being found not guilty in a criminal case by reason of insanity. That leaves out an array of people who probably shouldn’t be sold a gun—suicide risks, for instance. …

Defining the “Bad Guns.” President Obama will include an assault-weapons ban on his list of To Do’s for the Congress and the administration on guns. Gun owners like to point out that it’s not entirely clear what an assault weapon is, other than that it looks scary.