"Can we prevent another Sandy Hook, and if so, how?"
Simply stated, there are three necessary ingredients for a Sandy Hook type event, a depraved state of mind in the perpetrator, a choice of murderous implement and a target of opportunity.
These three ingredients occur in a roughly linear progression. The murderer reaches the state of mind, selects his implement of destruction and then selects his target. To prevent similar tragedies interdiction at any of these three stages is fair game for discussion.
1. THE PERPETRATOR- The reason these rare events are so shocking is that we lack the ability to recognize utter depravity before it reaches the point of mass murder. If we had that capability, preventing another Sandy Hook would be a simple matter. But we don't, so are left with the final two steps in the murderous triptych.
2. THE IMPLEMENT- In the currently raging schism, we are largely focused on firearms. The political left chooses to step outside this linear progression (state of mind → implement → target) by preventing law-abiding, non-murderous citizens from possessing firearms on the dubious theory that restricting availability of firearms to law-abiding citizens will eventually limit firearm availability to non-law-abiding folks. This is analogous to outlawing automobiles for everybody because some weirdo plows his SUV into the local farmers' market. The only difference is that the right to possess firearms is specifically delineated in the Bill of Rights. It also neglects the idea that mass murderers can (and will) choose implements other than firearms (automobiles, flammables and machetes to name just three).
3. THE TARGET- In an ostensibly free society, it comes down to being prepared to protect innocent lives at the point of attack. Citizens as first responders prevented flight 92 from reaching D.C. on 9/11. Hardening cockpit doors and random air marshall presence has kept hijackers out of cockpits since then. We can do the same for our schools. We either are willing to do it or we are not. How will we choose?