Rather than wringing our hands, conducting marches and blaming people who have nothing to do with school shootings (President Trump, the NRA and gun owners), we should be looking for realistic actions we can take to actually prevent shootings at schools and other locations. There is no need to further restrict firearm ownership.
Some suggestions: secure schools like we do courts, airports and the Academy Awards. When someone is convicted of a crime prohibiting firearm possession the responsible agency reports it to the FBI (the Air Force failed this one). When law enforcement agencies, school administrators and others see red flags they need to take appropriate action (this was not done in Florida). Improve the judicial process to keep firearms from identified and confirmed mentally ill, dangerous people.
Doing these things will work, if approached and done seriously. One more option that should at least be discussed is to have armed people in schools, and other places, for when one of these killers slips through the cracks, and they will - no matter what we do.
Last - we need to stop looking to Washington, D.C., for help. The answers are available here and action needs to be taken here.