Motivations and techniques to kill masses vary from incident to incident so that there seems to be as many possible preventative solutions as there are incidents. Gun right advocates always respond to with more nonsense that the the most current incident would not have been prevented by such and such regulation and laws or proposed solutions or profiling personality types; therefore no solutions will work. There are copy cats and you can take it to the bank that the next mass killer now knows how to modify and use their weapons to do as much damage as possible it they did not know it before.
The Republican party has responded to calls for bringing gun control discussions in Congress with "now is not the time", refusing to set up a select committee on gun safety, and claiming "Democrats are using Vegas to politicize the issue". Shame on Democrats if they are, chimed in Colorado's Senator Cory Gardner. There seems to be some bi-partisan agreement however that bump stocks sales need to be outlawed.
Another response from gun rights advocates is that the single acceptable measure is to fund mental health services better . The Vegas shooter had no mental health red flags, which illustrates one limit of that approach. That we have a woefully inadequate mental health system is true, and intercepting wannabe mass killer patient is valuable and should be supported. However, as psychologists know they can predict who may be capable of doing it 50% of the time. Even if they do, we learned from the Aurora shooter history, a warning from the psychologist went nowhere. Protection of individual privacy rights trump the duty to warn as well in the rules and ethics of mental health professionals.
The GOP in control of Washington since January already tried to undermine access mental health services. The attempt to repeal and replace Obamacare with no required essential benefits overlooked the fact that insurance coverage of mental health was one of the benefits they tried to remove. In February, Donald Trump signed an executive order reversing an Obama era attempt to identify better those with mental health problems. Trump killed a regulation that would have required Social Security Administration to submit records of mentally disabled to the FBI database as part of the background check that would deny those the ability to buy guns. GOP reasoning: Some people who were "adjudicated as mental defective" were competent to own guns. In addition, the NRA lobbying has effectively scotched uniform background checks even though 74% of NRA members favor them. Stupid is as stupid does.