Only one question matters in the school violence debate: when a shooter is attempting to enter a school, what will be done to protect the lives of students and staff?

Asking what can be done to prevent mass school shootings is a secondary matter. Honest commentators — with the background and experience to know what they’re talking about — should be aware that in a constitutional republic, school shootings cannot be altogether prevented, and that gun control can have no effect. The worst school attack in history — in Beslan, Chechnya, leaving 300 dead and 700 injured — took place in a liberty-restricted state with democratic pretensions. Deterrence is possible, but not with past or current policies; the actual defense of the school during an incident is the heart of the debate.

At enormous expense, schools can be hardened, which may help to deter some potential killers, and which may slow down, to some degree, less intelligent and prepared killers. Unfortunately, “slow down” implies seconds, not minutes. Equally unfortunate: the money necessary to harden schools to the point of truly credible deterrence that could slow or stop killers to any meaningful degree is not available during the Obama economy.

Just recently, it was revealed that the Sandy Hook Elementary School killer needed only five minutes to shoot his way into the school and murder 20 children and six adults before killing himself. This fact is fodder for those wishing to ban “assault weapons” and standard capacity magazines so that future killers with five minutes will require a few seconds longer, or might only be able to kill 20 rather than 26. They miss the point, and many intentionally ignore more sensible proposals.

Former Navy SEAL and current educator John A. Czajkowski proposes a solution that embraces the recommendation of the NRA: place armed security in every one of the 100,000-plus American schools. However, he generally opposes the arming of school staff:

Although I grew up very comfortable with the responsible use of firearms as a boy and then later professionally, I still can’t support arming teachers first when there are still so many other more proactive opportunities for improving our security. Arming teachers is far down my list of recommendations for improving security, per balancing return on investment and risk assessment. Although I am entirely comfortable with the idea at a personal level, the difficulty of applying Kant’s universal imperative makes me hesitate to adopt an armed teacher paradigm.

Only one policy can credibly deter school shooters, will cost little or nothing, and will provide the maximum chance to limit — or even to eliminate — the loss of life when an attack on a school occurs: arming school staff.

When school design, security cameras, hardened doors and glass, magnetic door locks, and every other security measure have failed — as they did at Sandy Hook — and when a killer is seconds from firing, what is that school prepared to do at that moment to prevent any loss of life? Unless they are taking affirmative steps to arm staff so multiple people will always be present and prepared to immediately engage an armed attacker, the schools tacitly admit they are willing to accept a death toll of some size. This, in exchange for “feeling safe” rather than being safe.

NRA chief Wayne LaPierre and Czajkowski’s approach — using trained, armed personnel focused on school security — is not unreasonable, but it is impractical and embraces several faulty assumptions.

La Pierre would even demand federal funds for the purpose. Even so, some schools — usually larger high schools and some middle schools — do have school “resource” or “liaison” officers, who are usually certified law enforcement officers provided by local agencies.  Some schools share an officer from time to time, but most schools have none. This is so for practical and insurmountable reasons. Moreover, those few officers do not function as most of those supporting this concept believe.

These officers are essentially small-town police, responsible for all law enforcement functions in and around their assigned schools. They are generally present only during normal school hours, but must be absent for a wide variety of reasons: court, job-related errands, transporting arrestees, mandatory training, medical appointments, and vacation. At those times, they are virtually never replaced, and they are seldom present for extracurricular activities.

Further, it is not their job to principally focus on building security. And because there is only one of them per school — if that — the chance they will be present at the time and place an attack occurs is small. If no one else is armed, they are better than nothing, but are not the answer.

Most schools don’t have these liaison officers and never will; it’s too expensive. Their salaries, whether paid by their agency, their school, or some combination, come from the taxpayers, an increasingly scarce funding source. Affordably putting more of them in schools is wishful thinking.